546 PHILOSOPHY OF ZOOLOGY. 



which cover it when at rest, the groove, in which it is con- 

 tained when exerted, and the two spiculjE, with reversed 

 serratures at the summit, which inflict the wound. The 

 two tubular glands, which secrete the poison, take their 

 rise in the abdomen, unite to form the bag, from which 

 a duct issues, terminating at the base between the spiculae : 

 these, by uniting laterally, form a groove, by which the 

 poison is conveyed to the bottom of the wound. But, be- 

 sides these means of preserving life, many species are so vi- 

 vacious, that they will live long without food, and even 

 without air, and suffer sad mutilation before the vital spark 

 be extinguished. Among the Crustacea and arachnida, am- 

 putated hmbs ai'e even readily reproduced. 



The annulose animals with articulated feet are conve- 

 niently divided by means of the characters furnished by the 

 organs of respiration. 



Order I. — Branchial aerating organs. 



This order includes the class Crustacea of modern na- 

 turalists. Their external covering is usually crustaceous 

 or coriaceous. The antennae, in general, exceed two in 

 number. The situation of the gills furnishes the charac- 

 ters for the next subdivision. 



Section I. — Malacostraca. 



Branchiae at the base of the eight pair of legs, and con- 

 cealed underneath the border of the shield. 



The body appears to consist of a shield and tail above. 

 The shield is destitute of sutures, is incorporated with the 

 head, and supports anteriorly the two eyes, the antennae, 

 and the snout. Below, the thorax and abdomen are incor- 

 porated. The mouth is seated under the snout. The feet 

 amovmt to eight pair, the three first of which are converted 

 into auxiliary maxillae, while the remaining five pair are 



