448 MANUAL OF ZOOLOGY SECT. 



veloped in some cases. Most Reptiles have both upper 

 and lower eyelids and a nictitating membrane. The greater 

 number of the Geckos and all the Snakes constitute ex- 

 ceptions, movable eyelids being absent in both these 

 groups. In the Chamaeleons there is a single circular 

 eyelid with a central aperture. 



The middle ear is absent in the Snakes, though a 

 columella auris is present, embedded in muscular and 

 fibrous tissue. 



Developed in close relation to the epiphysis there is in 

 many Lizards (Lacerta, Varanus, Anguis^ Grammatophora 

 and others) and in Hatteria, a remarkably eye-like organ 

 fae pineal eye (Fig. 255), which is situated in a foramen of 

 the cranial roof immediately under the integument, and 

 covered over by a specially modified, transparent scale. 

 Like the epiphysis itself, the pineal eye is developed as a 

 hollow outgrowth of the roof of the diencephalon ; the distal 

 end of this becomes constricted off as a hollow sphere 

 while the remainder becomes converted into a nerve. The 

 nerve degenerates before the animal reaches maturity, so 

 that the organ would appear though evidently, from its 

 structure, an organ of sight to have now entirely or 

 nearly lost its function. 



Though fertilisation is always internal, most Reptilia are 

 oviparous, laying eggs clothed in a tough, parchment-like 

 or calcified shell. These are usually deposited in holes and 

 left to hatch by the heat of the sun. In the Crocodiles they 

 are deposited in a rough nest and guarded by the mother. 

 In all cases development has only progressed to a very early 

 stage when the deposition of the eggs takes place, and it is 

 only after a more or less prolonged period of incubation that 

 the young, fully formed in almost every respect, emerge 

 from the shell and shift for themselves. Many Lizards, 



