Part 5

Fig. 25. A. Ovum from the same ovary as fig. 21, containing in the yolk three peculiar bodies, similar in appearance to the two small bodies in the germinal vesicle. B. Germinal vesicle of a large ovum from the same ovary, containing a body of a strikingly similar appearance to those in the body of the ovum in A. Zeiss E, ocul. 2. _Picric acid._

Fig. 26. Section of the ovary of a young female of _Scyllium stellare_ 16-1/2 centimetres in length. The ovary is exceptional, on account of the large size of the stroma ingrowths into the epithelium. Zeiss C, ocul. 2. _Osmic acid._

Fig. 27. Ovum of _Scyllium canicula_, 5 mm. in diameter, treated with osmic acid. The figure illustrates the development of the yolk and a peculiar mode of proliferation of the germinal spots. Zeiss A, ocul. 2.

Fig. 28. Small part of the follicular epithelium and egg membranes of a somewhat larger ovum of _Scyllium canicul_a than fig. 22. Zeiss D D, ocul. 2.

Fig. 29. The same parts as in fig. 28, from a still larger ovum. Zeiss D D, ocul. 2.

Fig. 30. Ovum of Raja with follicular epithelium. Zeiss C, ocul. 2.

Fig. 31. Small portion of a larger ovum of Raja than fig. 30. Zeiss D D, ocul. 2.

Fig. 32. Follicular epithelium, &c., from an ovum of Raja still larger than fig. 31. Zeiss D D, ocul. 2.

Fig. 33. Surface view of follicular epithelium from an ovum of Raja of about the same age as fig. 33.

Fig. 34. Vertical section through the superficial part of an ovary of an adult Raja to shew the relation of the pseudo-epithelium to the subjacent stroma. Zeiss D D, ocul. 2.

PLATE 26.

COMPLETE LIST OF REFERENCE LETTERS.

_do._ Developing ovum. _fc._ Cells which will form the follicular epithelium, _fe._ Follicular epithelium. _ge._ Germinal epithelium. _mg._ Malpighian body. _n._ Nest of cells of the germinal epithelium. _nd._ Nuclei in the act of dividing. _o._ Permanent ovum. _ov._ Ovary. _po._ Primitive ovum. _t._ Tubuliferous tissue, derived from Malpighian bodies.

Fig. 35. Transverse section through the ovary of an embryo rabbit of eighteen days, hardened in osmic acid. The colours employed are intended to render clear the distinction between the germinal epithelium (_ge._) and the tubuliferous tissue (_t._), which has grown in from the Wolffian body, and which gives rise in the male to parts of the tubuli seminiferi. Zeiss A, ocul. 2.

Fig. 35A. Transverse section through a small part of the ovary of an embryo from the same female as fig. 35, hardened in picric acid, shewing the relation of the germinal epithelium to the subjacent tissue. Zeiss D D, ocul. 2.

Fig. 35B. Longitudinal section through part of the Wolffian body and the anterior end of the ovary of an eighteen days' embryo, to shew the derivation of tubuliferous tissue (_t._) from the Malpighian bodies, close to the anterior extremity of the ovary. Zeiss A, ocul. 1.

Fig. 36. Transverse section through the ovary of an embryo rabbit of twenty-two days, hardened in osmic acid. It is coloured in the same manner as fig. 35. Zeiss A, ocul. 2.

Fig. 36A. Transverse section through a small part of the ovary of an embryo, from the same female as fig. 36, hardened in picric acid, shewing the relation of the germinal epithelium to the stroma of the ovary. Zeiss D D, ocul. 2.

Figs. 37 and 37A. The same parts of an ovary of a twenty-eight days' embryo as figs. 36 and 36A of a twenty-two days' embryo.

Fig. 38. Ovary of a rabbit five days after birth, coloured in the same manner as figs. 35, 36 and 37, but represented on a somewhat smaller scale. _Picric acid._

Fig. 38A. Vertical section through a small part of the surface of the same ovary as fig. 38. Zeiss D D, ocul. 2.

Fig. 38B. Small portion of the deeper layer of the germinal epithelium of the same ovary as fig. 38. The figure shews the commencing differentiation of the cells of the germinal epithelium into true ova and follicle cells. Zeiss D D, ocul. 2.

Fig. 39A. Section through a small part of the middle region of the germinal epithelium of a rabbit seven days after birth. Zeiss D D, ocul. 2.

Fig. 39B. Section through a small part of the innermost layer of the germinal epithelium of a rabbit seven days after birth, shewing the formation of Graafian follicles. Zeiss D D, ocul. 2.

Figs. 40A and 40B. Small portions of the middle region of the germinal epithelium of a rabbit four weeks after birth. Zeiss D D, ocul. 2.

Fig. 41. Graafian follicle with two ova, about to divide into two follicles, from a rabbit six weeks after birth. Zeiss D D, ocul. 2.

EXPLANATION OF PLATES 27 AND 28. (XIII. p. 618.)

COMPLETE LIST OF REFERENCE LETTERS.

_ao._ Aorta. _cv._ Cardinal vein. _gl._ Glomerulus. _gr_1. First groove of head-kidney. _gr_2. Second groove of head-kidney. _gr_3. Third groove of head-kidney. _ge._ Germinal epithelium. _mrb._ Malpighian body. _me._ Mesentery. _md._ Müllerian duct. _r_1. First ridge of head-kidney. _r_2. Second ridge of head-kidney. _r_3. Third ridge of head-kidney. _Wd._ Wolffian duct. _x._ Fold in germinal epithelium.

PLATE 27.

SERIES A. Sections through the head-kidney at our second stage. Zeiss 2, ocul. 3 (reduced one-third). The second and third grooves are represented with the ridge connecting them, and the rod of cells running backwards for a short distance.

No. 1. Section through the second groove.

No. 2. Section through the ridge connecting the second and third grooves.

No. 3. Section passing through the same ridge at a point nearer the third groove.

Nos. 4, 5, 6. Sections through the third groove.

No. 7. Section through the point where the third groove passes into the solid rod of cells.

No. 8. Section through the rod when quite separated from the germinal epithelium.

No. 9. Section very near the termination of the rod.

No. 10. Last section in which any trace of the rod is seen.

SERIES B. Sections passing through the head-kidney at our third stage. Zeiss C, ocul. 2. Our figures are representations of the following sections of the series, section 1 being the first which passes through the anterior groove of the head-kidney.

No. 1 SECTION 3. No. 8 SECTION 13. " 2 " 4. " 9 " 15. " 3 " 5. " 10 " 16. " 4 " 6. " 11 " 17. " 5 " 8. " 12 " 18. " 6 " 10. " 13 " 19. " 7 " 11. " 14 " 20.

The Müllerian duct extends through eleven more sections.

The first groove (_gr_1.) extends to No. 3.

The second groove (_gr_2.) extends from No. 4 to No. 7.

The third groove (_gr_3.) extends from No. 11 to No. 13.

The first ridge (_r_1.) extends from No. 2 to No. 5.

The second ridge (_r_2.) extends from No. 8 to No. 11.

The third ridge (_r_3.) extends from No. 13 backwards through twelve sections, when it terminates by a pointed extremity.

FIG. C. Section through the ridge connecting the second and third grooves of the head-kidney of an embryo slightly younger than that from which Series B was taken. Zeiss C, ocul. 3 (reduced one-third).

The fold of the germinal epithelium, which gives rise to a deep groove (_x._) external to the head-kidney is well marked.

SERIES G. Sections through the rod of cells constituting the termination of the Müllerian duct at a stage in which the head-kidney is still present. Zeiss C, ocul. 2.

PLATE 28.

SERIES D. Sections chosen at intervals from a complete series traversing the peritoneal opening of the Müllerian duct, the remnant of the head-kidney, and the termination of the Müllerian duct. Zeiss C, ocul. 3 (reduced one-third).

Nos. 1 and 2. Sections through the persistent anterior opening of the head-kidney (abdominal opening of Müllerian duct). The approach of the Wolffian duct to the groove may be seen by a comparison of these two figures. In the sections in front of these (not figured) the two are much more widely separated than in No. 1.

No. 3. Section through the Müllerian duct, just posterior to the persistent opening.

Nos. 4 and 5. Remains of the ridges, which at an earlier stage connected the first and second grooves, are seen passing from the Müllerian duct to the peritoneal epithelium.

No. 6. Rudiment of the second groove (_gr_2.) of the head-kidney.

Between 6 and 7 is a considerable interval.

No. 7. All traces of this groove (_gr_2.) have vanished, and the Müllerian duct is quite disconnected from the epithelium.

No. 8. Rudiment of the third groove (_gr_3.).

No. 9. Müllerian duct quite free in the space between the peritoneal epithelium and the Wolffian duct, in which condition it extends until near its termination. Between Nos. 9 and 10 is an interval of eight sections.

No. 10. The penultimate section, in which the Müllerian duct is seen. A lumen cannot be clearly made out.

No. 11. The last section in which any trace of the Müllerian duct is visible. No line of demarcation can be seen separating the solid end of the Müllerian duct from the ventral wall of the Wolffian duct.

FIGS. E. and F. Sections through the glomerulus of the head-kidney from an embryo prior to the appearance of the head-kidney. Zeiss B, ocul. 2. A comparison of the two figures shows the variation in the thickness of the stalk of the glomerulus. E. Section anterior to the foremost Malpighian body. F. Section through both the glomerulus of the head-kidney and that of a Malpighian body. The two are seen to be connected.

SERIES H. Consecutive sections through the hind end of the Müllerian duct, from an embryo in which the head-kidney was only represented by a rudiment. (The embryo was, perhaps, very slightly older than that from which Series D was taken.) Zeiss C, ocul. 3 (reduced one-third).

No. 1. Müllerian duct is without a lumen, and quite distinct from the Wolffian wall.

No. 2. The solid end of the Müllerian duct is no longer distinct from the internal wall of the Wolffian duct.

No. 3. All trace of the Müllerian duct has vanished.

SERIES I. Sections through the hinder end of the Müllerian duct from an embryo of about the middle of the sixth day. Zeiss C, ocul. 2 (reduced one-third).

No. 1. The Müllerian duct is distinct and small.

No. 2. Is posterior by twelve sections to No. 1. The Müllerian duct is dilated, and its cells are vacuolated.

No. 3. Penultimate section, in which the Müllerian duct is visible; it is separated by three sections from No. 2.

No. 4. Last section in which any trace of the Müllerian duct is visible; the lumen, which was visible in the previous section, is now absent.

No. 5. No trace of Müllerian duct. Nos. 3, 4, and 5 are consecutive sections.

FIG. K. Section through the hind end of the abdominal opening of the Müllerian duct of a chick of 123 hours. Zeiss C, ocul. 2 (reduced one-third). It illustrates the peculiar cord connecting the Müllerian and Wolffian ducts.

EXPLANATION OF PLATE 29. (XIV. p. 644.)

COMPLETE LIST OF REFERENCE LETTERS.

_am._ Amnion. _ch._ Notochord. _ch´._ Notochordal thickening of hypoblast. _ep._ Epiblast. _hy._ Hypoblast. _m.g._ Medullary groove. _me.p._ Mesoblastic plate. _ne._ Neurenteric canal (blastopore). _pr._ Primitive streak.

SERIES A. Sections through an embryo shortly after the formation of the medullary groove. x 120[4].

Footnote 4: The spaces between the layers in these sections are due to the action of the hardening reagent.]

Fig. 1. Section through the trunk of the embryo.

Figs. 2-5. Sections through the neurenteric canal.

Fig. B. Surface view of a somewhat older embryo than that from which Series A is taken. x 30.

SERIES B. Sections through the embryo represented in Fig. B. x 120.

Fig. 1. Section through the trunk of the embryo.

Figs. 2, 3. Sections through the hind end of the medullary groove.

Fig. 4. Section through the neurenteric canal.

Fig. 5. Section through the primitive streak.

Fig. C. Surface view of a somewhat older embryo than that represented in Fig. B. x 30.

EXPLANATION OF PLATES 30, 31, 32. (XVII. p. 668.)

PLATE 30.

COMPLETE LIST OF REFERENCE LETTERS.

_ch._ Cheliceræ. _ch.g._ Ganglion of cheliceræ. _c.l._ Caudal lobe. _p.c._ Primitive cumulus. _pd._ Pedipalpi. _pr.l._ Præoral lobe. _pp_{1}. _pp_{2}. _etc._ Provisional appendages. _sp._ Spinnerets. _st._ Stomodæum.

I-IV. Ambulatory appendages. 1-16. Postoral segments.

Fig. 1. Ovum, with primitive cumulus and streak proceeding from it.

Fig. 2. Somewhat later stage, in which the primitive cumulus is still visible. Near the opposite end of the blastoderm is a white area, which is probably the rudiment of the procephalic lobe.

Fig. 3_a_ and 3_b_. View of an embryo from the ventral surface and from the side when six segments have become established.

Fig. 4. View of an embryo, ideally unrolled, when the first rudiments of the appendages become visible.

Fig. 5. Embryo ideally unrolled at the stage when all the appendages have become established.

Fig. 6. Somewhat older stage, when the limbs begin to be jointed. Viewed from the side.

Fig. 7. Later stage, viewed from the side.

Fig. 7_a_. Same embryo as fig. 7, ideally unrolled.

Figs. 8_a_ and 8_b_. View from the ventral surface and from the side of an embryo, after the ventral flexure has considerably advanced.

Fig. 9. Somewhat older embryo, viewed from the ventral surface.

PLATES 31 AND 32.

COMPLETE LIST OF REFERENCE LETTERS.

_ao._ Aorta. _ab.g._ Abdominal nerve cord. _ch._ Cheliceræ. _ch.g._ Ganglion of cheliceræ. _ep._ Epiblast. _hs._ Hemispherical lobe of supra-oesophageal ganglion. _ht._ Heart. _l.l._ Lower lip. _m._ Muscles. _me._ Mesoblast. _mes._ Mesenteron. _mp.g._ Malpighian tube. _ms._ Mesoblastic somite. _oe._ OEsophagus. _p.c._ Pericardium. _pd._ Pedipalpi. _pd.g._ Ganglion of pedipalpi. _pr._ Proctodæum (rectum). _pr.c._ Primitive cumulus. _s._ Septum in abdomen. _so._ Somatopleure. _sp._ Splanchnopleure. _st._ Stomodæum. _su._ Suctorial apparatus. _su.g._ Supra-oesophageal ganglion. _th. g._ Thoracic ganglion. _v.g._ Ventral nerve cord. _y.c._ Cells derived from yolk. _yk._ Yolk. _y.n._ Nuclei of yolk cells.

I_g_-IV_g_. Ganglia of ambulatory limbs. 1-16. Postoral segments.

Fig. 10. Section through an ovum, slightly younger than fig. 1. Shewing the primitive cumulus and the columnar character of the cells of one half of the blastoderm.

Fig. 11. Section through an embryo of the same age as fig. 2. Shewing the median thickening of the blastoderm.

Fig. 12. Transverse section through the ventral plate of a somewhat older embryo. Shewing the division of the ventral plate into epiblast and mesoblast.

Fig. 13. Section through the ventral plate of an embryo of the same age as fig. 3, shewing the division of the mesoblast of the ventral plate into two mesoblastic bands.

Fig. 14. Transverse section through an embryo of the same age as fig. 5, passing through an abdominal segment above and a thoracic segment below.

Fig. 15. Longitudinal section slightly to one side of the middle line through an embryo of the same age.

Fig. 16. Transverse section through the ventral plate in the thoracic region of an embryo of the same age as fig. 7.

Fig. 17. Transverse section through the procephalic lobes of an embryo of the same age. _gr._ Section of hemicircular groove in procephalic lobe.

Fig. 18. Transverse section through the thoracic region of an embryo of the same age as fig. 8.

Fig. 19. Section through the procephalic lobes of an embryo of the same age.

Fig. 20_a_, _b_, _c_, _d_, _e_. Five sections through an embryo of the same age as fig. 9. _a_ and _b_ are sections through the procephalic lobes, _c_ through the front part of the thorax. _d_ cuts transversely the posterior parts of the thorax, and longitudinally and horizontally the ventral surface of the abdomen. _e_ cuts the posterior part of the abdomen longitudinally and horizontally, and shews the commencement of the mesenteron.

Fig. 21. Longitudinal and vertical section of an embryo of the same age. The section passes somewhat to one side of the middle line, and shews the structure of the nervous system.

Fig. 22. Transverse section through the dorsal part of the abdomen of an embryo of the same stage as fig. 9.

EXPLANATION OF PLATE 33. (XX. p. 714.)

Fig. 1. Transverse section through the pelvic fin of an embryo of _Scyllium_ belonging to stage P[5], magnified 50 diameters. _bp._ basipterygium. _br._ fin ray. _m._ muscle. _h f._ horny fibres supporting the peripheral part of the fin.

[Footnote 5: I employ here the same letters to indicate the stages as in my "Monograph on Elasmobranch

Fig. 2. Pelvic fin of a very young female embryo of _Scyllium stellare_, magnified 16 diameters. _bp._ basipterygium. _pu._ pubic process of pelvic girdle (cut across below). _il._ iliac process of pelvic girdle. _fo._ foramen.

Fig. 3. Pelvic fin of a young male embryo of _Scyllium stellare_, magnified 16 diameters. _bp._ basipterygium. _mo._ process of basipterygium continued into clasper. _il._ iliac process of pelvic girdle. _pu._ pubic section of pelvic girdle.

Fig. 4. Transverse section through the ventral part of the trunk of an embryo _Scyllium_ of stage P, in the region of the pectoral fins, to shew how the fins are attached to the body, magnified 18 diameters. _br._ cartilaginous fin-ray. _bp._ basipterygium. _m._ muscle of fin. _mp._ muscle-plate.

Fig. 5. Transverse section through the ventral part of the trunk of an embryo _Scyllium_ of stage P, in the region of the pelvic fin, on the same scale as fig. 4. _bp._ basipterygium. _br._ cartilaginous fin-rays. _m._ muscle of the fins. _mp._ muscle-plate.

Fig. 6. Pectoral fin of an embryo of _Scyllium canicula_, of a stage between O and P, in longitudinal and horizontal section (the skeleton of the fin was still in the condition of embryonic cartilage), magnified 36 diameters. _bp._ basipterygium (eventual metapterygium). _fr._ cartilaginous fin-rays. _pg._ pectoral girdle in transverse section. _fo._ foramen in pectoral girdle. _pe._ epithelium of peritoneal cavity.

Fig. 7. Transverse section through the pectoral fin of a _Scyllium_ embryo of stage P, magnified 50 diameters. _bp._ basipterygium. _br._ cartilaginous fin-ray. _m._ muscle. _hf._ horny fibres.

Fig. 8. Pectoral fin of an embryo of _Scyllium stellare_, magnified 16 diameters. _mp._ metapterygium (basipterygium of earlier stage). _me.p._ rudiment of future pro- and mesopterygium. _sc._ cut surface of a scapular process. _cr._ coracoid process. _fr._ foramen. _hf._ horny fibres.

Fig. 9. Skeleton of the pectoral fin and part of pectoral girdle of a nearly ripe embryo of _Scyllium stellare_, magnified 10 diameters. _mp._ metapterygium. _mes._ mesopterygium. _pp._ propterygium. _cr._ coracoid process.

EXPLANATION OF PLATES 34-42. (XXII. p. 738.)

LIST OF REFERENCE LETTERS.

_a._ Anus. _ab._ Air-bladder. _ab´._ Aperture of air-bladder into throat. _ac._ Anterior commissure. _af._ Anal fin. _al._ Alimentary canal. _ao._ Aorta. _ar._ Artery. _au._ Auditory pit. _b._ Brain. _bc._ Body-cavity. _bd._ Bile duct. _bd´._ Aperture of bile duct into duodenum. _bl._ Coalesced portion of segmental ducts, forming urinogenital bladder. _bra._ Branchial arches. _brc._ Branchial clefts. _c._ Pyloric caæca. _c´._ Apertures of caæca into duodenum. _cb._ Cerebellum. _cdv._ Cardinal vein. _ce._ Cerebrum: in figs. 47A and B, anterior lobe of cerebrum. _ce´._ Posterior lobe of cerebrum. _cf._ Caudal fin. _cn._ Centrum. _ch._ Choroidal fissure. _crv._ Circular vein of vascular membrane of eye. _csh._ Cuticular sheath of notochord. _cv._ Caudal vein. _d._ Duodenum. _dc._ Dorsal cartilage of neural arch. _df._ Dermal fin-rays. _dl._ Dorsal lobe of caudal fin. _dlf._ Dorsal fin. _e._ Eye. _ed._ Epidermis. _ep._ Epiblast. _fb._ Fore-brain. _fe._ Pyriform bodies surrounding the zona radiata of the ovum, probably the remains of epithelial cells. _gb._ Gall-bladder. _gd._ Genital duct. _gl._ Glomerulus. _gr._ Genital ridge. _h._ Heart. _ha._ Hæmal arch. _hb._ Hind-brain. _hc._ Head-cavity. _hpd._ Hepatic duct. _hm._ Hyomandibular cleft. _hop._ Operculum. _hy._ Hypoblast; in fig. 10, hyoid arch. _hyl._ Hyaloid membrane. _ic._ Intercalated cartilaginous elements of the neural arches. _in._ Infundibulum. _ir._ Iris. _is._ Interspinous cartilage or bones. _iv._ subintestinal vein. _ivr._ Intervertebral ring of cartilage. _k._ Kidney. _l._ Lens. _lc._ Longitudinal canal, formed by union of the vasa efferentia. _lin._ Lobi inferiores. _ll._ Ligamentum longitudinale superius. _lr._ Liver. _lt._ Lateral line. _ly._ Lymphatic body in front of kidney. _m._ Mouth. _mb._ Mid-brain. _mc._ Medullary cord. _mel._ Membrana elastica externa. _mes._ Mesorchium. _mn._ Mandible. _md._ and _mo._ Medulla oblongata. _ms._ Mesoblast. _na._ Neural arch. _na´._ Dorsal element of neural arch. _nc._ Notochord. _nve._ Network formed by vasa efferentia on inner face of testis. _od._ Oviduct. _od´._ Aperture of oviduct into bladder. _ol._ Nasal pit or aperture. _olf._ Olfactory lobe. _op._ Optic vesicle. _op ch._ Optic chiasma. _opl._ Optic lobes. _op th._ Optic thalami. _or ep._ Oral epithelium. _ov._ Ovary. _p._ Pancreas. _pc._ Pericardium. _pcf._ Pectoral fin. _pch._ Pigmented layer of choroid. _pf._ Peritoneal funnel of segmental tube of mesonephros. _pfp._ Peritoneal funnel leading into pronephric chamber. _pg._ Pectoral girdle. _plf._ Pelvic fin. _pn._ Pineal gland. _po._ Primitive germinal cells. _pr._ Mesoblastic somite. _prc._ Pronephric chamber. _prn._ Pronephros. _pr n´._ Opening of pronephros into pronephric chamber. _pt._ Pituitary body. _py._ Pyloric valve. _pz._ Parietal zone of blastoderm. _r._ Rostrum. _rb._ Rib. _rc._ Rectum. _s._ Spleen. _sc._ Seminal vessels passing from the longitudinal canal into the kidney. _sd._ Suctorial disc. _sg._ Segmental or archinephric duct. _sgt._ Segmental tubules. _sh._ Granular outer portion of the sheath of the notochord in the vertebral regions. _smx._ Superior maxillary process. _snc._ subnotochordal rod. _so._ Somatic mesoblast. _sp._ Splanchnic mesoblast. _spn._ Spinal nerve. _spv._ Spiral valve. _st._ Stomach. _st._ Seminal tubes of the testis. _sup._ Suctorial papillæ. _t._ Testis. _th._ Thalamencephalon. _thl._ Lobes of the roof of the thalamencephalon. _tr._ Trabeculæ. _ug._ Urinogenital aperture. _v._ Ventricle. _ve._ Vasa efferentia. _vh._ Vitreous humour. _vl._ Ventral lobe of the caudal fin. _vmt._ Ventral mesentery. _vn._ Vein. _vs._ Blood-vessel. _vsh._ Vascular sheath between the hyaloid membrane and the vitreous humour. _vth._ Vesicle of the thalamencephalon. _x._ Groove in epiblast, probably formed in process of hardening. _y._ Yolk. _z._ Commissure in front of pineal gland. _zr._ Outer striated portion of investing membrane (zona radiata) of ovum. _zr´._ Inner non-striated portion of investing membrane of ovum. I. Olfactory nerve. II. Optic nerve. III. Oculomotor nerve. V. Trigeminal nerve. VIII. Facial and auditory nerves.

PLATE 34.

Figs. 1-4. Different stages in the segmentation of the ovum.

Fig. 1. Ovum with a single vertical furrow, from above.

Fig. 2. Ovum with two vertical furrows, from above.

Fig. 3. Side view of an ovum with a completely formed blastodermic disc.

Fig. 4. The same ovum as fig. 3, from below, shewing four vertical furrows nearly meeting at the vegetative pole.

Figs. 5-10. External views of embryos up to time of hatching.

Fig. 5. Embryo, 3.5 millims. long, third day after impregnation.

Fig. 6. Embryo on the fifth day after impregnation.

Fig. 7. Posterior part of same embryo as fig. 6, shewing tail swelling.

Fig. 8. Embryo on the sixth day after impregnation.

Fig. 9. Embryo on the seventh day after impregnation.

Fig. 10. Embryo on the eleventh day after impregnation (shortly before hatching).

Fig. 11. Head of embryo about the same age as fig. 10, ventral aspect.

Fig. 12. Side view of a larva about 11 millims. in length, shortly after hatching.