24-0 SYSTEMATIC ARRANGEMENT. 



Phasnhdae certainly surpass all others in length. 

 Many of them measure half-a-foot from one ex 

 tremity to the other, and one of them, (P. gigas) 

 occasionally attains the length of about nine inches. 

 The resemblance of the narrow bodied kinds to a small 

 branch, is in many instances remarkably close, and 

 this in connection with other peculiarities, is no 

 doubt often the means of preserving them from the 

 attacks of other animals. Were this not the case, 

 they would fall an easy prey to their enemies, for 

 they are ill fitted to act on the defensive, and the 

 slowness of their movements affords but little chance 

 of escape by flight. Among the other peculiarities 

 alluded to, may be mentioned the spines with which 

 many of them are beset, particularly on the head 

 and thorax. As an example of this sort, P. cornu- 

 tum, a large species, may be cited, whose frontal 

 horns give such a formidable expression to its head, 

 that it would not be supposed a priori to belong to a 

 creature of perfectly innoxious habits. 



To enable them to cling to branches, and " drag 

 their slow length along," the tarsi in general are much 

 developed ; the basal joint especially is often long 



