VERTEBRATES FROM A CRUSTAOBAN-LIKE ANCESTOR. 443 



Fig. 14. — Transverse section through the region of the cerebellum, to show 

 the arrangement of the cells of the arachnoidal tissue and the ventral and 

 dorsal blood-sinuses. Boro-picro-carmine preparation. 



Fig. 15. — Magnified drawing of the cells of the arachnoidal tissue. Carmine 

 preparation. 



Fig. 16. — Cells of arachnoidal tissue. Osmic preparation from the same 

 series as Fig. 20, 



Fig. 17. — Transverse section through the epicliordal portion of the brain, 

 to show the increase of the pigment round the brain. Carmine preparation 

 of Ammoccetes 28 mm. in length which had been kept alive in the laboratory 

 for a year. a. Pigment bearing blood-corpuscles in the ventral sinus. 



Fig. is. — Magnified drawing of red blood-corpuscles, to show formation of 

 pigment in them. a. Normal blood-corpuscle, h. Commencing pigment 

 formation round the nucleus. 



Fig. 19. — Transverse section through the spinal cord of a full-grown 

 Ammoccetes. 



Fig. 20 a, b, c, d. — From the same series as Fig. 6 and Fig. 8, to show the 

 relation of the dorsal pineal eye and its nerve to the surrounding tissue, and 

 also the shape of the cavity of the eye. en. Place of entrance of nerve, 

 c. nas. Nasal cartilage. 



Fig. 21. — Horizontal section through the ventral pineal eye of a full-grown 

 AmmoccEtes. Boro-picro-carmine preparation, glil^. Main portion of left 

 ganglion habenuls. ghl^. Optic portion of left ganglion habenulse. fi. Fold 

 of pia mater which separates the ventral eye from the left ganglion habenulse, 

 and is perforated by the bundle of fibres (/.) in one place. 



Fig. 22. — Magnified drawing of a portion of the pineal eye represented in 

 Figs. 20 « — A. The drawing is taken from the section immediately following 

 20 <i as we pass in the direction of 20 c, to show the nature of the contents of 

 the central cavity, and the arrangement of the lines of pigment. 



Fig, 23. — Ends of the nerve-end ceils of a lateral eye of Euscorpius. 

 From Lankester and Bourne, fig. 5. 



Fig. 24. — Section across the nerve-end cells of a lateral eye of Euscorpius, 

 showing the cuticular rods. From Lankester and Bourne, fig. 6, 



Fig. 25. — Termination of nerve-end cells bearing rhabdites of an Acilius 

 larva. From Grenacher. 



Fig. 26. — Horizontal section through the dorsal pineal eye of a full-grown 

 Ammoccetes, to show the relation of the eye to the walls of the cranial cavity. 

 Carmine preparation, nas. Nasal cavity. 



Fig. 27. — From same series as Fig. 21, to show the structure of the dorsal 

 pineal eye and of the right ganglion habeuulfc. The dotted lines represent 



