192 W. BALDWIN SPENCEE. 



pineal stalk formed ; this would be attached primitively to the 

 posterior end, and the bending of the cells of the vesicle wall 

 (fig. 21) make it appear as if a subsequent drawing down of 

 the stalk to the ventral surface had taken place. In the 

 specimens examined the stalk is seen to end anteriorly some- 

 what sharply against the under surface of the vesicle, at any 

 rate, in this part none of its fibres could be traced into the 

 cells above, though, as the specimens examined were not 

 specially preserved for histological purposes, it is quite possible 

 that with fresh ones a connection might be demonstrated. 

 Posteriorly, however, where the drawing down of the wall 

 occurs the fibres and cells are in connection with each other. 



The pineal stalk itself is a very definite structure, running from 

 the under surface of the vesicle downwards and slightly backwards, 

 till just without the parietal foramen, where it joins the hollow 

 epiyhysial stalk running backward to the roof of the thalamence- 

 phaloD. In structure it resembles closely that of Hatteria. 



Gecko verus. 



Neither in the adult nor in the embryo is there the slightest 

 external trace of the organ, the skin being tuberculated and 

 capable of being lifted up from the head without remaining 

 attached in the position of the parietal foramen. There is no 

 discernible trace of the latter : in lizards in which it is present 

 the skin cannot be removed wholly from the surface of the head. 



Sections show that the epiphysis is a well-marked structure 

 in Platydactylus arising from the roof of the thalamence- 

 phalon and running straight upwards till it comes into contact 

 with the roof of the cranial cavity. This portion corresponds 

 to the proximal part of the structure in other forms, and appa- 

 rently the pineal stalk, which usually runs forward from this 

 along the dura mater, as well as the distal portion modified into 

 the pineal eye, are both absent in Gecko. The epiphysis is hollow 

 and its cavity gradually increases in size as it passes further from 

 the roof of the brain and approaches the skull, against which 

 it ends blindly ; there is no differentiation in its walls, so far as 

 could be discerned, to form an optic vesicle. 



