CLASS OF CEUSTACEA. 



433 



same individual, or compare them in distinct species. Those 

 of the first rings, in general, have relations to the functions of 

 animal life, and carry eyes or form antennae ; the following 

 surround the mouth, and serve for the prehension or the 

 division of the food (y, 122, 123) ; those of the middle por- 

 tion of the body constitute limbs for locomotion, and those 

 placed still further back have very variable uses, but serve in 

 general for respiration or reproduction : finally, this long 

 series terminates generally by one or more pairs of limbs, 

 arranged to serve as fins. 



The head, or rather the cephalic portion of the body, carries 

 the eyes, the antenna?, and the buccal appendages : sometimes 

 it is divided into several distinct rings, as in the squilli or 

 shrimps, for example (3?ig. 429); although generally it presents 

 no such separation, being formed only of a single segment, 

 which seems to represent seven rings, confounded together. 

 Sometimes it is moveable, and distinct from the thorax 

 (Fig. 419) ; at other times, on the 

 contrary, it is united to this second 

 portion of the body, which in its 

 turn is composed in certain species 

 of rings articulated together, but 

 distinct; in others, united into a 

 single mass. 



The antenna? are almost always 

 composed of two pairs, and consti- 

 tute in general very elongated fili- 

 form horns, or what at least re- 

 sembles them. The limbs are con- 

 nected in pairs with the different 

 thoracic rings ; there are frequently 

 seven pairs : in the cloporte (Fig. 

 419), the crevettes (prawns of rivu- 

 lets), and the talytri, for example ; 

 but at other times, as may be seen 

 in the crabs (Fig. 420) and the 

 ecrevisses (craw-fish, lobsters, Fig. 

 122), their number is reduced to 

 five pairs only ; for the appen- 

 dages, which in the first case formed the four anterior limbs, 

 are then turned to other uses, and transformed into organs 

 of mastication. There exist also very great differences in 

 their structure ; in some Crustacea they are wholly foli- 

 F F 



Fig. 422 . Hippe (Hippa). 



