210 W. BALDWIN SPENCER. 



which on nearing the eye bulb breaks up into numerous 

 branches which ramify (figs. 27 and 30, B. v.) amongst the 

 pigment cells encasing the eye. 



Zootoca vivipara. 

 The presence and structure of the eye in this form has been 

 described to a certain extent by Leydig, though he failed to 

 recognise its connection with the epiphysis, and did not apply 

 to it the name of eye. The presence of deep pigment in the 

 specimen examined makes it impossible to describe in detail 

 the structure of the retina. Pigment is also thickly deposited 

 in the skin, but it is seen in section to end abruptly on each 

 side of the parietal foramen ; so thick is the layer of pigment 

 that no light, save for this provision, could possibly reach the 

 pineal eye. 



The eye has the usual form of a hollow vesicle with the lens 

 anteriorly, lying immediately beneath the specialised scale. 

 Pigment runs from the proximal part of the epiphysis to the 

 eye, but, as far as could be told, the latter is separated from the 

 brain. 



The eye is present in early stages, before any definite indi- 

 cation of the parietals can be distinguished ; in an embryo 

 whose head measured 6 mm. in length, the eye is a prominent 

 object on the dorsal surface of the head, immediately beneath 

 the skin. It is flattened in the dorso-ventral line so that the 

 cavity is small; anteriorly the lens is differentiated and its 

 cells are perfectly continuous with those of the vesicle behind, 

 which are being transformed into the retinal elements, though 

 the fine pigment granules already deposited throughout their 

 substance (and absent from those of the lens) render it dif- 

 ficult to distinguish the difl'ereut elements; facing into the 

 vesicle, however, the rods can be seen around which the pig- 

 ment granules are thickest; external to these lie spherical 

 elements massed closely together and not yet separated into 

 definite layers. These may very probably be regarded as the 

 nuclei of the cells whose internal parts are becoming trans- 

 formed into rods. The eye appears to be connected with the 



