BULLETIN 



USTSTITTJTIE] 



VOL. 17. SALEM: APR., MAY, JUNE, 1885. Nos. 4-6. 



ON THE CARAPAX AND STERNUM OF DECAPOD CRUSTACEA.* 



BY HOWARD AYERS, Ph.D., Ann Arbor, Mich. 



The determination of the homology of the carapax and 

 sternum among the Crustacea is rendered difficult by the 

 endless variety of forms assumed by their constituent parts, 

 and the consequent perplexing differences in the relation 

 of these parts to each other. Before stating the conclu- 

 sions and arguments in favor of the solution at which I 

 have arrived after a study of several forms chiefly of the 

 Decapod type, it may conduce to clearness to give in a 

 few words, the main facts and conclusions of the previous 

 writers on this subject. 



Although Huxley (1) is the latest writer who expresses 

 views on the homologies of the Crustacean carapax, he 

 offers no new explanation but adheres to the old conception 

 of a fusion of the terga of the fourteen anterior somites 

 into a carapax. He writes (in describing Astacus flu- 

 viatilis) "The carapace, therefore, corresponds in position 

 with the terga and tergal halves of the pleura of all the 

 somites which are thus reflected into it, and these somites 



* This paper was prepared in the Mus. Comp. Zool., under the direction of 

 Prof. W. Faxon, in the college year 1S82-83. 



KSSKX INST. BULLETIN, VOL. XVII. 7 (49) 



