io8 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



domen. The cephalothorax is covered above and on the sides 

 by the firm carapace, which is divided by the transverse cervical 

 suture into parts corresponding to the head and thorax. The 

 compound eyes are situated at the ends of two short stalks which 

 arise just beneath the rostrum, the anterior horn-like projec- 

 tion of the carapace. The segments of which the cephalo- 

 thorax is composed are so fused together that they are not 

 readily distinguished, but each segment of the body bears a 

 pair of appendages and by the position and character of these 

 appendages the different regions can be determined. Each 

 of these appendages, except the antennae, consists of a basal 

 part from which arises two branches made up of one or more 

 segments modified to perform certain functions. 



Just below the eyes is the first pair of appendages, the 

 antennules, in the base of each of which is an organ formerly 

 supposed to be an auditory organ but now known to be an 

 organ of equilibration. These aid the animal in keeping the 

 body in a proper position while swimming. Next come the 

 antenna, or feelers, which, like the antennules, are provided 

 with fine hairs which aid in the sense of touch and perhaps of 

 smell. The green gland lies at the base of the antennae. It is 

 probably an excretory organ with functions similar to the 

 kidneys of higher animals. 



Next comes the group of appendages surrounding the mouth, 

 the mandibles, two pairs of maxilla and three pairs of maxilli- 

 peds. The mandibles are hard and jaw-like. The second 

 maxillae have a large paddle-like structure, the scaphognathite, 

 which extends back over the gills in the branchial chamber, 

 the space between the lower part of the carapace and the body- 

 wall. The movements of this appendage keep the currents of 

 water flowing through the gill chamber. The maxillipeds are 

 appendages of the thorax. The first pair of legs is much 

 larger than the others, the terminal segments being developed 

 into strong pincers or chela. Each pair of legs, except the 

 last, bears gills which extend up into the branchial chamber. 

 In the basal segments of the last pair of legs of the male are the 

 genital pores. In the female the genital pores are in the 

 basal segments of the second pair of walking-legs. In the 



