NATURAL HISTORY. 335 



" A tortoisr, introduced here (Lambeth Palace) in 1G33, lived 

 till the year 1753, and possibly might have continued much 

 longer, had it not been for the carelessness of the gardener." 



PENNANT. 



1003. Why arc reptiles so called ? 



The term is derived from a Latin word repo, I creep ; since the 

 imperfection of the legs and feet in some cases, and the total 

 absence of these members in others, necessarily entail a creeping 

 movement to enable the animal to move along the ground. 



1004. Why are turtles and tortoises covered with hard external 

 shells? 



Because they are destitute of bony skeletons within, and the horny 

 covering is made to answer all the purposes of the usual osseous 

 structure. 



But, besides this, they are defenceless animals, except so far as 

 the shell affords a retreat to the head, legs, and tail, which are 

 withdrawn within the shell upon the occurrence of any danger. 



1005. It may appear at first sight that there is a great affinity between the 

 armour, or rather box, in which the tortoise is enclosed, and the coat of mail with 

 which many quadrupeds are covered, as, for instance, the armadillo (416). But 

 there is this important difference : the coat of mail in the latter quadruped is a 

 simple horny addition to the skin itself, resting upon, and supported by, processes 

 of the skeleton ; whereas the osseous shell of the tortoise is part and parcel of the 

 skeleton itself, which is so modified as to protect the internal organs, enclosing them 

 as in a casket, which is covered either with horny plates variously arranged, 

 or with a tough leathery skin.* 



1006. IVhy do the cheeks of tortoises and turtles appear to be 

 frequently distended ? 



Because they swallow air instead of breaking it by the ordinary 

 process. The jaws being firmly closed, the cavity of the mouth is 

 enlarged by the drawing down of the root of the tongue ; and into 

 the vacuum thus formed the air rushes through the nostiils. The 

 free part of the tongue is then applied to the. posterior openings of 

 the nostrils, so as to stop them ; the gullet is also closed, the root 



the tongue is elevated, the broad muscles of the throat contract, 



Knight's " Museum of Animated Nature." 



