STRUCTURE OF LIZARDS 7OI 



not, as In the frog, play an important part in the respiratory 

 movements. In some lizards (Chamaeleon and Geckos) the 

 lungs are prolonged in air-sacs, suggesting those of Birds 

 (Fig. 411). 



Excretory system. — The paired kidneys lie in the 

 extreme posterior region of the abdominal cavity, and 

 extend a little farther back than the level of the cloaca. 

 Each is furnished with a very short ureter. In the male the 

 ureters unite with the vasa deferentia ; in the female they 

 open separately into the cloaca. Into the cloaca opens also 

 a large thin-walled " urinary bladder " ; this is a remnant of 

 the foetal allantois, and has no functional connection with 

 excretion. The urine is semi-solid, and consists largely of 

 uric acid. 



Reproductive system. — In the male the testes are two 

 white oval bodies suspended in a dorsal fold of mesentery. 

 Along the inner surface of each runs the epididymis, which 

 receives the vasa efferentia, and is continuous posteriorly 

 with the vas deferens. The two vasa deferentia, after 

 receiving the ureters, open by small papillae into the cloaca. 

 In connection with the cloaca there is a pair of eversible 

 copulatory organs, postero-lateral in position. 



In the female the ovaries occupy a similar position to 

 that of the testes in the male. The oviducts open far 

 forward by wide ciliated funnels ; as they pass backward 

 they show a gradual increase in cross-section, but there 

 is no line of demarcation between oviducal and uterine 

 portions. Posteriorly, the oviducts open into the 

 cloaca. 



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

 left. In many of the males the Wolfi&an body is well developed. 

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

 well illustrated by Lacerta vivipara, Anguis fragilis, Seps, etc., 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 I-acertilians 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 hm.bs. 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. 



