THE DEVELOPMENT OF LEPIDOSIREN PARADOXA. 457 



c. Part of a transverse section of Stage 35, cutting the palato-ptcrvgoid 

 tooth germs longitutiinally. Letters as before, and b.v. Blood- 

 vessel ; b. Bony trabecule. Zeiss A, oc. 4. 



D. Part of the preceding section under a higher power (Zeiss 3 mm. 



apochrom., oc. 2) to show the minute structure of the dentine 

 which is being formed, and also the distinctness of the enamel 

 layer. 



E. Part of btclion similar to a andu, but from Stage 3G. Zeiss A, oc. 2. 



F. Part of similar section from Stage 38. Zeiss A, oc 2. 



B'iG. 8. — Illustrating the brain of Lcpidosiren as seen from the dorsal 

 side. 



A. Stage 31 + . Reconstruction Zeiss a*, oc.2. The thalameiiccphalon 



and mesencephalon are not yet marked off from one another. 



B. Stage - 35. Reconstruction Zeiss a*, oc. 2. 

 c. Stage 38. Dissection. 



D. Adult. 



and. Auditory vesicle or capsule, c.h. Cerebral hemispheres. 

 d.g. Dorsal root ganglion, ep. Pineal body. /./. Pore-limb. 

 mes. Mesencephalon, n.a. Neural arch. olf. Olfactory capsule. 

 th. Thalamencephalon (the line stops over the left habenular 

 ganglion). v.lV. Roof of fourth ventricle. 



Cranial Nerves. — I. Olfactory. II. Optic. III. Oculo-motor. 

 IV. Pathetic. V. Trigeminal. V.' Ophthalmic division. 

 V.^ Maxillary division. V.^ Mandibular division. VII. Pacial : 

 Nil, h.m- Hyomandibular ; Vil, /«/. Lateral; VII, 5.jo. Supe- 

 rior palatine; VII and X, r.c. Commissure connecting lateral 

 portions of VII and X. VIII. Auditory. IX. Glosso-pharyu- 

 geal. X. Vagus: X, hiL Lateral trunk; \, lat.ffaiif/. Lateral 

 ganglion ; X, vise. gang. Visceral ganglion. 



Fig. 9. — View of brain of adult from below. 



hyp. Hypophysis. /./. Inferior lobe. VI. Abducent. 



PLATE 27. 



Fig. 10. — The brain of Lepidosiren in side view, a, b, c, p, e, represent 

 reconstructions ; f, g, h, i, dissections. 



A. Stage 26. 



B. Stage 29 + . 

 c. Stage 30. 



