CRUSTACEA 135 



are the antennules about one fourth as long as the jointed 

 antenna? proper. On the lower surface of the basal joint 

 of each of these is the opening of the green glands or 

 kidneys. On the thorax are four pairs of long slender 

 walking legs, in front of which is a pair of very large legs 

 called chelipeds, terminating in pincers, the chelce. Anterior 

 to these are three pairs of small appendages, the maxillipeds, 

 or jaw feet, of use in feeding. 



The head proper shows in the mouth region a pair of 

 hard notched lateral moving mandibles and behind them 

 two pairs of leaflike maxillce. The second pair of maxillae 

 differs from the first pair in having a flat paddle-like 

 process, called gill bailer, used to bring the water forward 

 from the gill chamber, in which are the gills beneath the 

 carapace. On the ventral side of several segments of 

 the abdomen are small appendages, termed pleopods or 

 swimmerets, which carry the eggs in the female. Each 

 pleopod consists of a basal piece, the protopodite, and two 

 branches, the outer of which is the exopodite and the inner 

 the endopodite. This is the typical structure of a crusta- 

 cean appendage, but in many cases it is much modified 

 by use, as in the walking legs where the exopodite is 

 wanting. 



By pinning down the specimen in a waxed-bottom pan 

 full of water and cutting off the carapace and dorsal por- 

 tion of the abdomen, some of the structures shown in the 

 figure may be found. The male can be distinguished from 

 the female by the presence of the minute orifice of the 

 reproductive organ on the ventral side of the last leg near 

 its junction with the thorax. In the female the opening is 

 on the third leg from the last. 



