A CRAB 35 



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 anterior 

 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 sperm ducts 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, themiddle 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 it. Label all carefully. 



Remove all the viscera, taking care not to injure the brain and 

 the circumoesophageal nerves, and examine the nervous system. 

 The brain is just back of the eyes, as in the lobster or the cray- 

 fish, and is united with the ventral nerves by means of the lateral 

 circumoesophageal 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 mass, in the 

 shape of a ring, which occupies a central position in the cephalo- 

 thorax, and from which nerves radiate to the different append- 

 ages. The dorsoventral artery passes through this ring. Expose 

 the entire nervous system. 



Exercise 6. Draw a semidiagrammatic view of the nervous system, 

 being careful to represent accurately the nerves radiating from the 

 ganglionic ring and those going from the brain to the eyes and to 

 the antennae. 



