54 THE VOYAGE OF H.M.S. CHALLENGER. 



tail (T) is as yet only represented by a slight rounded prominence limiting the above 

 mentioned sinus posteriorly, and not yet exhibiting any trace of appendages. The 

 anterior extremity of the embryo is considerably broader and more evenly rounded 

 than the posterior, and exhibits most anteriorly two rounded areas (o), which, from analogy 

 with the embryos of the Podophthalmia, may be regarded as the ocular plates, as yet 

 wholly separated, but afterwards becoming confluent and at last cpiite obliterated. Behind 

 these plates the anterior lip (L) can be distinctly traced, and further back the bipartite 

 posterior lip or metastoma (I). On each side of the anterior lip two transverse 

 prominences occur, representing the antennulae (a 1 ) and antennae (a 2 ), the first of 

 which are the larger, and on each side of the posterior lip the mandibles (M) may be 

 traced as two rounded knobs. Further back two pairs of prominences, somewhat 

 different both from the preceding and succeeding ones, are seen, the anterior (m 1 ) 

 being unequally bipartite, the posterior («r) slightly tripartite at the free edge. These 

 prominences represent the two pairs of maxillae. Then follows a regular double series 

 of posteriorly pointing prominences, all of a quite similar appearance and unequally 

 bilobed at the end. The number of these prominences is seven pairs, 1 of which the 

 first (mp) represent the maxillipeds, the two succeeding the two pairs of gnathopoda 

 (gn 1 , gn 2 ), and the four posterior (jp 1 - p^) the four anterior pairs of legs, the last pair 

 not being formed until very late, even a considerable time after the young have left 

 the marsupial pouch. The two rounded lobes which all of these pairs of limbs exhibit, 

 may undoubtedly be regarded as the first indication of the two principal parts, the 

 endopodite and exopodite, and it is rather striking that even the first pair of gnatho- 

 poda, which never exhibit any trace of exopodites in the adult animal, do not differ in 

 this respect from the following limbs, and that, moreover, in all the embryos the two 

 posterior pairs (third and fourth pairs of legs) have also a similar bilobed form, although 

 these limbs in the female are cpiite simple. Immediately above the oral region on each 

 side a curved ridge or slight fold (C) may be traced, representing the first indication of 

 the carapace, and within the area limited below by this fold a rounded cellular body (A) 

 occurs, which ultimately becomes the liver, or caeca of the stomach. 



As may be seen from the above description of the embryo, the development of the 

 Cumacea differs materially from that of the Mysidae and other Podopthalmia in two 

 very important points; firstly, by the embryo exhibiting, while still enclosed within the 

 egg-membrane, a well-marked dorsal curvature, and secondly, by the last pair of legs 

 not being formed until a considerable time after the young have escaped from the 

 marsupial pouch. In both these respects the Cumacea agree, on the other hand, very 

 closely with the Isopoda. 



Habitat. — Eight more or less perfect specimens of this species were taken by the 

 dredge in the North Atlantic, off Nova Scotia, from a very considerable depth. 



1 In fig. 14, by a mistake, eight such pairs have been indicated instead of seven. 



