LIZARDS. 477 



" When the pectoral arch is complete, it consists of a supra-scapula, 

 scapula, coracoid (with precoracoid and epicoracoid elements), and two 

 clavicles, united by an interclavicle, which lies in the groove of the 

 sternum." 



In the pelvic girdle, the ilia are movably articulated to cartilages at 

 the end of the sacral ribs, the pubes (usually with a pre-pubic process) 

 and the ischia meet in median symphyses. 



Further Notes in regard to Lizards. 



, Many Lizards, such as the Chamseleons, exhibit in a remarkable degree 

 the power of rapidly changing the colour of their skin. This is due to the 

 fact that the pigment-cells or chromatophores contract or expand under 

 nervous control. The change of colour is sometimes advantageously pro- 

 tective, but it seems often to be merely a reflex symptom of the nervous 

 condition of the animals. 



In a few cases, e.g., some of the skinks, there are minute dermal 

 ossifications beneath the scales. 



In some, there are two aortic arches on each side, uniting with one 

 another and forming the dorsal aorta. A single epigastric vein collects 

 blood from the abdominal walls and from the bladder, and enters the 

 liver, like the anterior abdominal of the frog. 



In some Lizards (Chamseleons and Geckos), there are small air-sacs 

 connected with the lungs, suggesting those of Birds. 



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 vivifarus, 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 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. 



Classification of Lizards. — The order Lacertilia is usually divided into 

 about a score of families. 



In the geckos (Geckonidoe) the vertebras are biconcave or amphi- 

 ccelous, 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 : — Platydactyltis mauritanicus (S. Europe), Hemi- 

 dadylus in most warm countries, Ptyckozoon, with lateral webs of skin 

 which serve as parachutes. 



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



