16 HISTOEY OF CEUSTACEA. CHAP. III. 



Edriophthalma could be adduced in its support, as the 

 structure of this very coherent group seemed to be 

 almost irreconcilable with many peculiarities of the 

 Zoea. Thus, in my eyes, this point long constituted one 

 of the chief difficulties in the application of the Dar- 

 winian views to the Crustacea, and I could scarcely 

 venture to hope that I might yet find traces of this 

 passage through the Zoea-form among the Amphipoda 

 or Isopoda, and thus obtain a positive proof of the cor- 

 rectness of this conclusion. At this point Van Bene- 

 den's statement that a cheliferous Isopod (Tanais 

 Dulongii}, belonging, according to Milne-Edwards, 

 to the same family as the common Asellus aqua- 

 ticus, possesses a carapace like the Decapoda, directed 

 my attention to these animals, and a careful exa- 



Fig. 2.2 ; 



mi nation proved that these Isopods have preserved, 

 more truly than any other adult Crustacea, many of the 

 most essential peculiarities of the Zoece, especially their 



2 Tanais dubius (?) Kr. $ , magnified 25 times, showing the orifice 

 of entrance (x) into the cavity overarched by the carapace, in which 

 an appendage of the second pair of maxillae (/) plays. On four feet 

 (r, fc, I, ra) are the rudiments of the lamellae which subsequently form 

 the brood-cavity. 



