ADAPTATIONS TO SPECIAL ENDS 151 



on its back in order to terrify the intruder. If these gestures 

 fail to effect the desired end, the reptile throws itself headlong 

 into the water above which it generally takes its station. 



Chamaeleons when made angry by irritation either present 

 their lateral and broadest aspect to the intruder, or blow out 

 the whole body by inflating it with air, at the same time hissing 

 loudly. Evidently these actions are for the purpose of making 

 the creature appear as large, and therefore as dangerous-looking 

 as possible, and thus striking terror into the hearts of aggressors. 

 The most interesting point connected with these gestures is that 

 the inflation of the body is brought about by means of a special 

 modification in the structure of the lungs, and is therefore an 

 adaptation of deep significance. The lungs of chamaeleons, which 

 are very capacious, differ from those of other lizards by the 

 circumstance that, in place of being bag-shaped, they end in a 

 number of narrow blind sacs, which extend far down into the 

 body-cavity, thus permitting the inflation not only of the chest 

 but likewise of the entire body. Whether this peculiar structure 

 of the lungs was developed for the purpose of permitting the 

 periodical inflation of the body, or whether such inflation is a 

 secondary adaptation due to the peculiar structure of the lungs, 

 may be left an open question. In this place may be noticed the 

 peculiar lung-structure of snakes, although it has no connection 

 with either attack or defence, but is merely an adaptation to the 

 long and slender bodily form of these reptiles. The two lungs 

 are unequally developed ; the right forming a sausage-like 

 cylinder which extends a long way down the body-cavity, while 

 the left one is a very thin hollow bag of small size, with scarcely 

 any of the usual honey-comb cells in its posterior half or pos- 

 terior third, so that it merely serves the purpose of an air 

 reservoir and takes no active share in the work of respiration. 



Everyone who has had any experience of lizards in the 

 wild condition will be aware that in many species, and even in 

 all the members of certain families, the tail is extremely fragile 

 and apt to snap suddenly in twain when the reptile is startled 

 or seized. The slow-worm (Anguis fragilis), for instance, 

 exhibits this peculiar phenomenon to perfection, and takes its 

 specific name from the facility with which it can discard its caudal 

 appendage. When frightened or suddenly seized in the hand, 

 the slow-worm, as well as many kinds of four-limbed lizards, 



