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 axe 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 chameleons 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, G?-ammatophora > 

 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 



