174 HANDBOOK OF INVERTEBRATE ZOOLOGY. 



(iv.) The portion of soft integument which lies between 

 the joint of the appendage and the tergum is the epime- 

 ron. This can hardly be recognized in the abdomen of 

 the crab. 



c. The male abdomen (Figs. 91 and 103, ah), is made 

 up of four pieces. The first corresponds to the first in 

 the female abdomen ; the second is formed by the fusion 

 of the second, third, and fourth rings ; while the third 

 corresponds to the fifth in the female, and the fourth to 

 the sixth. 



d. The male abdomen carries only two pairs of append- 

 ages, modified to form copulatory organs. 



e. In both sexes, the anus is placed upon the sternal 

 surface of the last abdominal somite. 



f. Make sketches of the male and the female abdomen, 

 showing these points. 



g. The Sternal Plastron. 



This is the broad, shield-shaped ventral skeleton of that 

 portion of the body which lies between the basal joints of 

 the five pairs of legs. Its surface is excavated in the 

 middle line for the reception of the abdomen. It is made 

 up of the united sterna and episterna of a number of 

 somites.* 



1. On its exposed surface notice five distinct sutures or 

 folds ; the lines of union between the posterior six of the 

 eight sterna (Fig. 91, s'-s''"), which enter into it. 



2. Wedged in between the outer ends of these sterna, 

 notice the episteima of the corresponding somites ; each 



* As the critical discussion of disputed points would be out of place 

 in this work, I have followed Milne Edwards in this description. His 

 terminology is the one which the student will meet in text-books and 

 lectures, and it does not seem advisable to create confusion by changes, 

 which, to the beginner, would seem arbitrary and meaningless. 



iHI 



