AN AMPHIPOD 43 



Study the appendages, beginning with the free thoracic ones. 

 With fine needles separate the legs and observe the gills 

 attached to the posterior borders. How many bear gills ? In 

 the female observe the brood-sac when it is present ; it is formed 

 by plate-like projections of the inner side of certain thoracic 

 feet. In the abdomen observe the biramous appendages ; they 

 bear no gills. The cephalic appendages are those typical of 

 Crustacea. In front of the mouth is a median lip called the 

 labrum, which, however, is not an appendage. Then come the 

 mandibles and two pairs of maxillae. The pair of appendages, 

 the maxillipeds, belonging to the first thoracic somite (which is 



fused with the cephalic somites) form a kind of lower lip. 





 Exercise 2. Construct a table of somites and appendages similar 



to that made use of in the dissection of the lobster or the 



crayfish. (See page 29.) 



