MORPHOLOGY OF THE CUMACEA. 



The morphological relationship of the Cumacea to the other groups of Crostacea is 

 rather obscure, and hence their systematic position has been much disputed. At first 

 they were even considered by some of the greatest authorities, as Milne-Edwards, Dana, 

 and L. Agassiz, as merely larval forms of higher Crustacea. Both Kroyer and Groodsir, 

 however, clearly showed them to be adult animals, and thus it was necessary to range 

 them within the carcinological system. These two authors regarded them as lower forms 

 of Macrura, whereas Dohm and others seem to be more inclined to associate them with 

 the Edriophthalmia (Isopoda). I think their affinity to either of these groups is so verv 

 slight as to justify the establishment of a distinct order for their reception. More 

 recently. Dr. Boas has discussed the affinity of the ditferent groups of the Malacostraca 

 from a phylogenetic point of view, and has been led to the conclusion that the Cumacea 

 are very nearly related to the Mysidse, and may have descended directly firom this group 

 of Schizopoda. "With this view I cannot, however, fuUy agree. It is undoubtedly a 

 matter of great difficulty, if not quite impossible, to arrange the recent groups of 

 Crustacea in a genealogical manner, as most of them in all probabilitv represent very 

 diverging branches, the origin of which from one or a few ancestral forms may go back 

 to a very remote period of geological time. The Cumacea would seem to represent such 

 an isolated branch, and cannot, of course, in my opinion, strictly be derived from any of 

 the recent groups. 



As to the external appearance of these peculiar Crustacea, one would perhaps be most 

 inclined to associate them with the Podophthabnia, but on closer examination we find 

 them to difl'er materially in many points, and even in that important character from 

 which the name of the above-mentioned group has been derived. The anatomical details 

 present, on the whole, a peculiar mixture of the podophrhalmous and edriophthalmous type, 

 and the development is rather unlike that of the Podophthalmia, and evidently much 

 more similar to that of the Isopoda. The oral parts, which are generally regarded as 

 afi'ording highly important characters, I find — in contradiction to the opinion of Dr. Boas 

 — verv different from those in the Mvsidse. and on the whole constructed on the same 

 general type as in the Isopoda. On the other hand, the presence of well-developed 



