452 



H. BOSCHMA. 



developed paraphysis is found immediately before the latter. 

 Almost quite the same arrangement and structure of these organs 

 is found in Platydactylus muralis L., an allied species, in which 

 the anatomy and development of the parietal organ is described 



FIG. 4. Ptychozoon homalocephalum, newly-hatched specimen. Longitudinal 

 section of a part of the brain. Haematoxylin-Delafield, eosin. X 43- ch, com- 

 missura habenularis superior; cp, commissura posterior; e, epiphysis cerebri; M, 

 mesencephalon; p, paraphysis; 5, skin; T, telencephalon; v, velum transversum. 



at length by Melchers (1900). Besides that from the newly- 

 hatched Ptychozoon (with a head-length of n mm.) a section of 

 which is shown in the figure, another series of longitudinal sec- 

 tions was made from a younger stage, measuring 9 mm. from 

 snout to occiput. The conditions found here make it highly 

 probable that the development of these organs in Ptychozoon is 

 quite the same as that in Platydactylus muralis. 



In the case of Ptychozoon the above-cited hypothesis put 

 forward by Fuchs agrees fairly well with the facts. The data 

 available in the literature, however, are often in contradiction 

 with this hypothesis. In Platydactylus mauretanicus the parietal 

 organ is absent and yet this lizard assumes a dark color in the 

 light and becomes light-colored in the dark. On the contrary 

 Stellio caucasicus has a well-developed parietal eye and notwith- 

 standing that the animal becomes light-colored in the light and 

 dark in dark surroundings (cp. Studniczka, 1905, and Fuchs, 

 1914). These two instances already prove that there is insuffi- 

 cient evidence to uphold the above-mentioned hypothesis of 

 Fuchs. 



