474 



CHUSTACEA. 



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 (Mi/sis) or 

 at the same time also on the median and anterior (Lophogaster) 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 (Euphau#ia\ 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 

 (maxillse and first niaxillipeds) 

 soon appear as small promi- 

 nences. The large carapace 

 of the Nauplius, which is 

 curved forwards round the 

 base of the antennas where 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- 

 zoan and then of the Zorea 

 (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. 



Fam- Mysidas. Mi/sis -culgaris Thomps., M.jlc.ruosn 0. Fr. Mull., M. incrmte 

 Eacthk, Northern sens Rir'u-Ua JMwardxii Cls. 



FIG. 371. Mysis oi-nJafa. Female roth brood 

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

 vesicle. 



