450 MANUAL OF ZOOLOGY sect. 



is always of small size, except in the Crocodilia (Fig. 270), 

 in which it is comparatively highly developed, and consists 

 of a median and two lateral lobes. 



The eyes are relatively large, with a cartilaginous sclerotic 

 in which a ring of bony plates is developed in some cases. 

 Most reptiles have both upper and lower eyelids and nicti- 

 tating membrane. The greater number of the geckos and 

 all the snakes constitute exceptions, movable eyelids being 

 absent in both these groups. In the chamseleons there is 

 a single circular eyelid with a central aperture. 



The middle ear is absent in the snakes, though a colu- 

 mella 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 — 

 the pineal eye (Fig. 271), 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 



