CRUSTACEA. 45 



In order to see the nervous system of the lobster, all 

 the organs and muscles must be removed. The nerves of 

 the abdomen will be exposed first, as those of the ccpha- 

 lothorax are entirely concealed by a hard, limy secretion, 

 which forms a " false bottom" to this region of the body. 

 When this has been cut away, a double white cord will be 

 seen extending along the floor of the body, and connect- 

 ing thirteen ganglia. The anterior ganglion is the largest. 

 and is the lobster"s •• brain." * 



Allusion was made to the moulting of the lobster 

 when speaking of crustacean deformities. This process 

 of moulting, or of shedding the shell, is one of the 

 important characteristics of animals encased in articu- 

 lated armor like Crustacea and Insecta, it being, in 

 fact, the only way in which provision is made for the 

 increase in si/e of the body by growth. The lobster 

 sheds its shell whenever the old one becomes too small. 

 The number of moults in a given time varies with age, 

 the young lobster shedding its shell oftener, while the 

 large one is supposed to moult, at least, once a year. 

 When the animal is aged it ceases to moult, and bar- 

 nacles, mollusks, and other creatures have time to be- 

 come attached and grow on the shell. 



Only three descriptions have been given of the oper- 

 ation, and these were written by naturalists who received 

 their information from unscientific witnesses. The 

 mode of moulting varies, the animal either crawling out 

 of his shell, as the crayfish does between the carapace 



* For a full description of the anatomy of the lobster and 

 crayfish, see Huxley, "Anatomy of Invertebrated Animals"; 

 Huxley, "The Crayfish"; Packard, "Manual of Zoology"; 

 Kolleston, " forms of Animal Life." 



