THE PINEAL SYSTEM OF AMPHIBIA 227 



which lives in the subterranean waters of Carniola and Dalmatia, is in its 

 natural state described as being of " fleshy whiteness and transparency." 

 The absence of pigment in the skin and its presence in the epithelium of 

 the pineal organ appear to indicate a more feebly inherited tendency 

 towards the formation of pigment in the skin and a marked tenacity of the 

 inherited character with respect to the deposit of pigment in the epithelium 

 of the end vesicle of the pineal organ. On the other hand, it may be 

 argued that the pigment in the epithelium of the pineal organ is simply due 

 to chemical changes occurring in a degenerate tissue ; but since the pig- 

 ment is strictly limited to the epithelium of the pineal organ and is not 

 found in the surrounding mesodermal tissue and other parts of the brain, 

 nor in the body generally, this interpretation does not seem to be the 

 correct explanation of its presence in the pineal organ. 



A paraphysis (Fig. 160) is usually well developed in the Urodela, 

 and may appear as a simple tubular diverticulum or it may be branched 

 and glandular in appearance. 



The parietal foramen which is present in the skull of certain extinct 

 Urodeles has disappeared in living forms, e.g. in the newt (Molge cristata), 

 W. K. Parker, and Typhlototriton, H. Riese. In these, paired frontal and 

 parietal bones are separated by a cruciate suture. 



2. Apoda (Caecilia) 



The best-known example of this order is the slimy eel-like creature 

 Ichthyophis glutinosa, in which the lateral eyes are very small and are 

 imbedded in the skin. The adult animal has no limbs, but vestiges of 

 the hind limbs have been recognized in the embryo. The pineal organ 

 described in 1891 by Burckhardt is a small, pear-shaped hollow vesicle 

 the walls of which are infolded and the stalk attached to the roof of the 

 diencephalon just behind the habenular commissure. The paraphysis is 

 well developed and viewed in profile has the shape of a geological hammer, 

 the posterior limb of which overlaps and conceals the pineal organ. 

 Some fibres passed between the pineal organ and the roof of the dience- 

 phalon. Burckhardt was uncertain, however, whether these were nervous 

 or supporting in nature. The skull described by Sarasin, like that of other 

 living orders of Amphibia, shows no parietal foramen. 



In the genera Gymnopis and Herpele the lateral eyes have not only 

 sunk beneath the skin as in some other forms but they actually lie beneath 

 the bones of the skull. 



3. Anura (Acaudata) 



The development of the pineal organ in tailless amphibia is more 

 pronounced than in Urodela and Apoda, and in many at one period in their 

 development an end vesicle — stalk and proximal part — are distinguishable 



