LIZARDS. 577 



The right reproductive organ tends to be larger and in front of the 

 left. In many of the males, the Wolffian body is well developed. 

 Viviparous, or what is clumsily called ovo-viviparous, parturition is 

 well illustrated by Zootoca viviparus, Angztis fragilis, Seps, &c., but 

 most lay eggs with more or less calcareous shells. In Trachydosaurus 

 and Cyclodus the embryo seems to absorb food from the wall of the 

 uterus. It is likely that Lacertilians existed in Permian ages, but their 

 remains are not numerous before the Tertiary strata. 



Many instructive illustrations of evolutionary change are afforded by 

 lizards. Thus there are numerous gradations in the reduction of the 

 limbs, from a decrease in the toes to entire absence of limbs. The 

 diverse forms of tongue and the varied positions of the teeth are also 

 connected by gradations. From the variations of the wall lizard (Lacerta 

 muralis], Eimer elaborated most of his theory of evolution. 



Some Families of Lacertilia* 



The class includes great variety of form. 



In the Geckos (Geckonidre) the vertebrae are biconcave or amphi- 

 coelous, the tongue is short and fleshy, the eyelids are rudimentary, the 

 teeth are pleurodont, the toes bear numerous plaits, by means of which 

 they adhere to smooth surfaces. The Geckos have been observed to eat 

 their own young and even their own tails. The name Gecko indicates 

 their call. Examples : Platydactylus mauritantcus (S. Europe), Hemi- 

 dactylus in most warm countries, Ptychozoon, with lateral webs of skin 

 which serve as parachutes. 



The Agamas (Agamidse) are acrodont lizards common in the eastern 

 hemisphere. Examples : Agama; Draco, with the skin extended on 

 long prolongations of five or six posterior ribs; Chlamydosaurus, an 

 Australian lizard, with a large scaled frill around the neck ; Moloch, 

 another Australian form bristling with sharp spikes. 



The Iguanas (Iguanidae) are pleurodont lizards, represented in the 

 warmer parts of the New World. Examples : Iguana, an arboreal 

 lizard, with a large distensible dewlap ; Amblyrhynchus or Oreocephalus 

 cristatus, a marine lizard confined to the Galapagos Islands ; Basiliscus, 

 in S. Mexico, with none of the marvellous qualities of the mytho- 

 logical basilisk ; Anolis, the American chamseleon, with powers of 

 rapid colour change; Phrynosoma, the American "horned toad," with 

 numerous horny scales, and a collar of sharp spines suggesting in 

 miniature that of some of the extinct Reptiles. 



The slow worms (Anguidse), are limbless lizards, with serpentine 

 body, long tail, rudimentary girdles and sternum. The British species, 

 Anguis fragilis, is neither blind nor poisonous ; the tail breaks very 

 readily ; the young are hatched within the mother. The American 

 " glass snake " Opheosaurus ventralis is in many ways like our slow 

 worm. 



The poisonous Mexican lizard (Heloderma suspectuiii) measures over 

 a foot in length, and is covered with bead-like scales. Its bite is 

 poisonous, and rapidly fatal to small Mammals. It is interesting to 

 find poisonous powers like those of many serpents exhibited by this ex- 

 ceptional lizard. 



The water lizards (VaranidcE) are large semi-aquatic forms of carni- 

 37 



