42 CRUSTACEA. 



seen farther on. Thus it appears that it is not the law 

 of capitalization, but the effort to obtain food in the 

 most suitable way. and to meet the requirements of the 

 laws of equilibrium, which concentrates the growth in 

 some of the regions and appendages, and warps or 

 suppresses others through disuse. The animal thus 

 becomes able to balance itself upon the smallest num- 

 ber of supports possible for its type of structure, and 

 also acquires the greatest attainable facility in moving 

 and turning on its appendages or supports, a result 

 which is essential to the perfect development of all the 

 higher forms of walking types. The equality of the 

 segments and the elongation of the body in the crawl- 

 ing types like the worms can be strongly contrasted 

 with this concentration. The equality of the efforts 

 made by each ring in the sinuous movements of the 

 body on the surface, or through the mud or ground, is 

 here evidently the cause of the similarity, just as the 

 equality of the abdominal rings in the lobster, and 

 their appendages from / 2 to f 5 inclusive, may be 

 attributed to their performance of identical functions 

 in the act of swimming.* 



Owing to the large size of the lobster, only a little 

 care and patience are needed to study the different 

 internal organs. In dissecting the animal, it is desir- 

 able to have unboiled specimens. The scholars should 



* For information with regard to the specific effects of use, 

 see the following papers by John A. Ryder: "On the Laws of 

 Digital Reduction," American Naturalist, Oct., 1877; "On the 



Mechanical Ocnesis of Tooth Forms," Proceedings of the Acad, 

 of Nat. Sciences, Phila., 1S7S; also paper on the same subject 

 in American Naturalist, July, 1879. 





