290 CRUSTACEA. 



is the pharynx, and frequently covered by a sort of sub-labrum, styled 

 by M. Savigny the epipharyn<r. At other times, in the Hemiptera and 

 Diptera, the mandibles and maxillae are replaced by scaly pieces in the 

 form of sete, which are received in an elongated tubular sheath, that is 

 either cylindrical and articulated, or formed with more or less of an 

 elbow, and terminated by a kind of lips. In this case they constitute 

 a true proboscis. In others that also live by suction, the Lepidoptera, 

 the maxillae alone are greatly elongated and united, producing a tubular 

 setiform body, resembling a long, slender, and spiral tongue ; the re- 

 maining parts of the mouth are considerably reduced. Sometimes again, 

 as in many of the Crustacea, the anterior feet approach the maxilla-, 

 assume their form, and exercise part of their functions the latter are 

 then said to be multiplied. It may even happen that the true maxillae 

 become so much reduced, that the maxillary feet supply their place 

 altogether. Whatever be the modifications of these parts, however, they 

 can always be recognised and referred to a general type. 



CLASS I. 



CRUSTACEA. 



THE Crustacea are articulated animals, with articulated feet, re- 

 spiring by means of branchiae, protected in some by the t>orders of a 

 shell, and external in others, but which are not inclosed in special cavi- 

 ties of the body, and which receive air from openings in the surface of 

 the skin. Their circulation is double, and analogous to that of the 

 Mollusca. The blood is transmitted from the heart, which is placed on 

 the back, to the different parts of the body, whence it is sent to the 

 branchi, and thence back again to the heart. These branchiae, some- 

 times situated at the base of the feet, or even on them, and at others on 

 the inferior appendages of the abdomen, either form pyramids composed 

 of laminae in piles, or bristled with setae, or tufted filaments of simple 

 ones, and even appear in some cases to consist wholly of hairs. 



The Crustacea are apterous or deprived of wings, furnished with 

 compound eyes, though rarely with ocelli, and usually with four an- 

 tennae. They have mostly the Paecilopoda excepted three pairs of 

 jaws, the two superior ones, designated by the name of mandibles, 

 included ; as many foot-jams, the last four of which, however, in a 



