100 LABORATORY STUDIES IN ZOOLOGY 



convex dorsal portion as the tergum (meaning the "back"), 

 the lateral lobes as the pleura (singular, pleuron, meaning the 

 "side"), and the slender ventral bar as a sternum (" breastbone"). 



By removing the right appendage the following parts may be 

 made out: Its union with the segment is through a division 

 called the protopod. This consists of two portions, a very small 

 basal part, the coxopod, and a long distal part, the basipod. 

 From the basipod arise two flattened, many-jointed plates. The 

 outer of these is the exopod; the inner one near the median line, 

 the endopod. 



This type of appendage found on the abdominal segments is 

 called the forked or hiramous type of appendage. It is regarded 

 as the most primitive arthropod appendage, all other kinds having 

 been derived from such an appendage through modifications. 



The Remaining Abdominal Appendages. — Remove the remain- 

 ing appendages from the left side of the abdomen and arrange 

 them in the order of the segments to which they belong, beginning 

 at the cephalic end. The appendages of the second to fifth 

 somites, inclusive, in both sexes are quite similar to those of the 

 typical segment described above. There are the usual two 

 joints of the protopod comprising a short coxopod and a long 

 cylindrical hasipod. Both the endopod and exopod are present 

 as many jointed filaments, the former slightly longer than the 

 latter. The uropod comprises a very broad and thick single- 

 jointed protopod and two terminal oval plates which represent the 

 endopod and exopod. The latter is divided by a transverse 

 suture into two pieces. Noticeable differences exist between 

 the appendages of the first abdominal segment of the male and 

 female. In the male these appendages are stiffened and otherwise 

 modified so as to form an organ for transferring sperm to the 

 proper receptacle in the female. The first abdominal appendage 

 of the female is flexible and much reduced. 



Although wide variations in the appendages of the thorax and 

 head exist, they are nevertheless reducible to the same funda- 

 mental plan of structure as the abdominal appendages. 



The Appendages of the Thorax. — Beginning with the last 

 pair of walking legs, remove eight appendages from the left 

 side. Be sure to cut these close to the body wall so as not to 

 destroy their podohranchioe. The thoracic appendages include five 

 pairs of walking legs and three pairs of smaller appendages, the 

 maxilUpeds. Arrange these appendages in serial order for study. 



