332 ZOOLOGY SECT. 



(Chamseleons and Geckos) the scales are reduced and modified into 

 the form of minute tubercles or granules. In some Lizards special 

 developments of the scales occur in the form of large tubercles 

 or spines. Underlying the horny epidermal scales in some Lizards 

 (Skincoids) are series of dermal bony plates. In the integument 

 of the Geckos are numerous minute hard bodies which are inter- 

 mediate in character between cartilage and bone. 



In the Snake-like Amphisbsenians there are no true scales, with 

 the exception of the head shields, but the surface is marked out 

 into annular bands of squarish areas. 



In addition to the modification of the scales, the integument of 

 the Chamseleons is remarkable for the changes of colour which it 

 undergoes, these changes being due to the presence in the dermis 

 of pigment-cells which contract or expand under the influence of 

 the nervous system, reminding one of the integument of the 

 Cephalopoda. Less conspicuous and rapid changes of colour take 

 place in Anguis and in some Snakes. 



In the Chelonia scales, when developed, are confined to the 

 head and neck, the limbs and the tail ; but in all of them, with the 

 exception of the Soft Tortoises, both dorsal and ventral surfaces 

 are covered by a system of large horny plates. A series of horny 

 head-shields usually cover the dorsal surface of the head. Beneath 

 the horny plates of the dorsal and ventral surfaces are the bony 

 carapace and plastron, partly composed of dermal bones, but so 

 intimately united with elements derived from the endoskeleton 

 that the entire structure is best described in connection with the 

 latter (vide p. 335). 



In the Crocodilia, the whole surface is covered with horny plates 

 or scales, each usually marked with a pit-like depression about the 

 centre, those on the dorsal surface ridged longitudinally. Underlying 

 each of these, which are of epidermal derivation, is a thick pad of 

 dermal connective-tissue which, in the case of the dorsal scales, is 

 replaced by a bony scute. In the Caimans thin scutes also occur 

 under the ventral scales. 



A periodical ecdysis or casting and renewal of the outer layers 

 of the horny epidermis takes place in all the Reptilia with the 

 exception of the Crocodiles. Sometimes this occurs in a frag- 

 mentary manner ; but in Snakes and many Lizards the whole 

 comes away as a continuous slough. 



Endoskeleton. - - The vertebrae are always fully ossified. 

 Among recent forms the Geckos and Sphenodon (Fig. 992) are 

 exceptional in having the centra amphiccelous with remnants of the 

 notochord in the intercentral spaces. The rest of the recent 

 groups for the most part have the centra procoelous. In many 

 extinct forms the neural arches are not directly attached to the 

 bodies by bone (temnospondyly) : in recent forms there is a bony 

 union (stereospondyly) either through a suture or by fusion. 



