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.) 



Exercise 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 circumcesophageal connectives which pass on each 

 side of the oesophagus. There is, however, no long ventral 

 nerve cord with segmental ganglia, but a single large ganglionic 



