44 INVERTEBRATE ZOOLOGY 
of the first maxilliped which extends across the gills to the 
hinder part of the branchial chamber. 
Exercise 3. Construct a table showing the relation of the gills to 
the somites similar to that made use of in the dissection of 
the lobster or the crayfish. (See page 36.) 
Bxercise 4. Draw a diagrammatic cross section representing an 
outline of the body-wall in the region of the walking legs; 
show in this the relation which branchiostegites, legs, and 
gills bear to the body. 
Internal anatomy. With strong scissors and forceps remove 
the shell from the entire dorsal surface of the body, taking care 
not to injure the organs within. The arrangement of the organs 
will be seen to be similar to that in the crayfish or the lobster. 
The livers are a pair of extensive yellowish organs. The ante- 
rior portion of each of these passes laterally into the cavity 
of the branchiostegite; the posterior portion passes backward 
beneath the heart. In the male animal the testes are whitish 
organs which follow the course of the livers; the vasa deferentia 
are slender, coiled tubes which lie on each side of the heart. 
In the female animal the ovaries also accompany the livers; the 
oviducts are a pair of tubes which pass to the genital openings, 
the middle portion of each being expanded to form a large sac, 
the receptaculum seminis. 
Exercise 5. Draw an outline of the body and the organs as they 
lie in situ. Label all carefully. 
Remove all the viscera, taking care not to injure the brain 
and the circumcesophageal nerves, and examine the nervous 
system. The brain is just back of the eyes, as in the lobster 
or the crayfish, and is united with the ventral nerves by means 
of the lateral circumcsophageal connectives which pass on each 
side of the cesophagus. There is, however, no long ventral 
nerve cord with segmental ganglia, but a single large ganglionic 
