GENERAL ANATOMY. 5 



dages or limbs, though very various in form and 

 function, may all be reduced to three component 

 parts a basal portion or protopodite, which gives 

 support to two branches, termed respectively endo- 

 podite and exopodite. These parts are most clearly 

 developed in the swimming-feet, which are distinctly 

 made up of a peduncle and two branches, but in the 

 mouth organs the same structure may be traced, 

 though often modified to such an extent as to be 

 obscure and difficult of recognition. 



The cephalon in the Copepoda is composed of 

 six somites, its appendages being one pair of eyes, 

 two pairs of antennge, one pair of mandibles, one pair 

 of maxillas, and two pairs of foot-jaws ; the thorax 

 consists of five somites, and has five pairs of appen- 

 dages in the form of swimming-feet ; the abdomen 

 has no appendages, but consists of five somites 

 and terminates in a forked tail, which ought probably 

 to be considered as a sixth somite ; in the female the 

 first two abdominal somites are generally united, 

 forming one large genital segment with a pair of 

 vulvar apertures. In parasitic species the abdo- 

 men is often very much, reduced in size, both 

 as respects the number and bulk of its somites, and 

 this is the case also in some genera which are only 

 partially parasitic, as Corycaus, Acontiophorus, Arto- 

 trogus and others. As regards the cephalic appendages, 

 it must be noticed that the so-called two pairs of foot- 

 jaws are in reality portions of one and the same 

 somitic appendage, but having the appearance of 

 perfectly distinct organs they have come to be con- 



