AN AMPHIPOD 49 
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 maxille. 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 (page 35), leaving out of consideration, however, 
the protopodites, exopodites, and endopodites. 
