THE ORGANS OF THE OUTER GERM-LAYER. 



432 



the dermal scutes acquire a special condition and form, and, above all 

 are transparent. 



In regard to the particular form of the organ, there are essential!} 

 three types to be distinguished. 



In many Reptiles, e.g., in Platydactylus, the pineal gland has the 

 same structure as in Sharks : a small peripheral vesicle, which is 



schb p st bl x 



sh 



Fig. 244. Diagrammatic longitudinal section through the brain ofChameleo vulgaris with the 

 pineal organ, which is separated into three portions, a vesicular, a cord-like, and a tube-like 

 portion, after BALDWIN SPENCER. 



schb, Parietal bone with the foramen parietale ; p, pigment of the integument ; st, cord-like 

 middle portion of the epiphysis ; bl, its vesicular terminal portior* : x, transparent region 

 of the integument ; grh, cerebrum ; sh, optic thalamus ; v 3 , third ventricle, which is 

 continued \ipwards into the tube- like initial portion (^4) of the epiphysis. 



enclosed in the parietal foramen, is lined with ciliated cylindrical 

 cells, and is connected with the roof of the between-brain by means 

 of a long, hollow stalk. 



In other Reptiles, as in the Chameleon, the organ is differentiated 

 into three portions (fig. 244): first into a small closed vesicle (bl), 

 which lies under a transparent scale (x) in the foramen parietale 

 and IB lined with ciliated epithelium ; secondly into a solid cord 



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