498 LACERTII.IA CHAP. 



Most Autosauri are capable of changing colour. In most of 

 them this faculty is restricted to the assumption of paler or darker 

 tints owing to the shifting of the colouring matter contained in 

 the chromatophores. In others new, often vivid colours are the 

 result. The mechanism is described in detail in the Chameleon 

 on pp. 570 and 574. 



Pigment is deposited either directly in the upper strata of 

 the cutis, just below the Malpighian layer, or it is contained in 

 chromatophores. The latter are imbedded in the deeper . layers 

 of the cutis, and send out movable contractile processes, in 

 wliich their pigmented protoplasm is conveyed towards or away 

 from the surface. The only colours available are black, red, yellow, 

 and white, with their combinations of grey and brown. The 

 white pigment consists of guanin -salts. Blue and green are 

 structural colours, not due to pigment. The same can no longer 

 be said of the Ophidia, since Boulenger has observed accidentally 

 that green Tree-snakes (e.g. Dryoyhis) give the alcohol in which 

 they are kept the colour of green Chartreuse. 



Digestive organs. — The tongue is very variably developed, 

 and affords good taxonomic characters. It is always furnished 

 witli many tactile, or with gustatory, corpuscles. When the 

 tongue is very long and narrow it is generally forked, and in 

 these cases, for instance in the Yaranidae, is almost entirely used 

 as a sensory organ. In others, especially where it is broad, it 

 assists in catching the food, and in the Chameleons it has 

 attained a most elaborate development (see p. 569). 



Salivary glands are restricted to labial glands. In Heloderma 

 those of the lower jaw are transformed into poison-glands, an 

 analogy to what prevails in the poisonous snakes. The intestinal 

 canal is longest in the herbivorous forms ; the rectum sometimes 

 possesses a short blind sac or caecum. 



The cloaca of the Saiu'ia is somewhat modified ; instead of 

 the Coprodaeum, Urodaeum, and Troctodaeum forming three 

 successive chambers, the urodaeum is practically reduced to its 

 dorsal half, forming a dorsal recess between the two. other 

 chambers. The Coprodaeum is constricted into several successive 

 chambers, and is always well shut off from the urodaeum ])y a 

 strong sphincter. The urodaeum receives the urinary excretions, 

 which are mostly chalky white and are rather consistent instead of 

 being fluid. The riglit and left oviducts also open into it. The vasa 



