268 INTEODUCTION TO ZOOLOGY. 



of membranous pigment, or colouring matter, so arranged 

 that both may be visible at the same time ; or that the lower 

 layer may appear in varying proportions amid the upper ; or 

 that it may be altogether concealed beneath it. This mechan- 

 ism is similar to that which exists in some of the Cuttle-fish, 

 to whose changes of colour we have already referred (Part I., 

 p. 190). 



The Lizards, which are regarded as the true types or repre- 

 sentatives of the order, do not belong to any of the families 

 yet mentioned, but to the Lacertidoe. These have long, 

 slender, forked tongues, and are the attractive and nimble 

 reptiles which greet the eye of the traveller in France and 

 Italy. The family is not confined to Europe, some of its 

 members are found in each of the four quarters of the globe. 

 It is to this group that the two species of English Lizard be- 

 long — Lacerta agilis and Zootoca vivipara. Between them 

 a difference exists similar to that which has been mentioned 

 in the two species of Snakes (p. 263). The larger Lizard 

 (L. ogilis) is oviparous ; the smaller (Z. vivipara) brings 

 forth her young alive : or, to speak more correctly, is ovo- 

 viviparous.* 



Perhaps no one circumstance connected with their economy 

 is more sui'prising, when seen for the first time, than the facihty 

 with which the tail separates from the body. Great is the 

 astonishmcnit of a person unacquainted with this peculiarity, 

 when he grasps the tail and finds it remaining in his hand, 

 while the swift-running reptile effects its escape. 



The following characteristic occurrence is narrated by Dr. 

 J. L. Drummond : — " Beinsf on the sea shore at Pulo Bav, in 

 Sardinia, and searching for specimens of natural history, I 

 observed a large Lizard running for shelter under a heap of 

 stones. I was just in time to seize it by the end of the tail ; 

 but suddenly the resistance made by the animal to my attempt 

 to di-ag it from its hiding place ceased, and I gave it up for 

 lost ; but as suddenly had cause for alarm myself, on seeing 

 what appeared to be a small Snake leaping with great agility 

 about my feet, and springing as high as my knee. I instantly 

 started out of its way, and watched it at a respectful distance, 

 when I found that it was the tail of the animal, which I was 

 not before aware could so easily separate." t 



* The meaning of this term has been already explained, vide p. 263. 

 t " First Steps to Anatomy," p. 86. 



