474 



CUUSTACEA. 



abdominal feet, of which the anterior may, moreover, be provided with 

 copulatory appendages, they are capable of a more rapid and perfect 

 locomotion than the females, to which fact corresponds again the 

 greater respiratory requirements and the possession of branchial 

 appendages in Siriella. 



Development. The females bear on the two posterior (Mysis) or 

 at the same time also on the median and anterior (Lo})hogaster) pairs 



of thoracic limbs lamella?, 

 which form a brood pouch, in 

 which, as in the Arthrostraca, 

 the large eggs undergo their 

 embryonic development. In 

 other cases (Eup/uwtsia), the 

 development proceeds by meta- 

 morphosis. The young Eu- 

 phausia is hatched as a Nau- 

 plius larva, on which the three 

 following pairs of appendages 

 (maxilla? and first maxillipeds) 

 soon appear as small promi- 

 nences. The large carapace 

 of the Nauplius, which is 

 curved forwards round the 

 base of the antenna? w r here it 

 has a serrated edge, is the first 

 rudiment of the cephalo- tho- 

 racic shield, and beneath it, 

 at the sides of the unpaired 

 eye, the rudiments of the late- 

 ral eyes are visible. The larva 

 then, having moulted, assumes 

 first the form of the Proto- 

 zoa?a and then of the Zoa?a 

 (described by Dana as Calyp- 

 topis), which is however pro- 

 vided with only six pairs of 

 appendages and a long, already fully segmented, apodal abdomen. 

 In the numerous succeeding larval stages (Furcilia, Cyrtopia) the 

 remaining appendages are successively developed. 



FIG. 371. Mysis ccutata. Female with brood 

 lamellae (after G. O. Sars). Gb, Auditory 

 vesicle. 



Fam, Mysidw. My 

 Eaetht, Northern seas 



x wtlyaris Thomps., M.flexuosa O. Fr. Mull., M. inermte 

 Siriella Edwardsii Cls. 



