THE EUPHAUSIACEA 



247 



second pair is modified and the terminal segments bear a group of 

 long serrated " harpoon-like " spines. In Nematobrachion, the details 

 of the raptorial limbs are very similar to those of Nematoscelis, but 

 it is the third pair that is modified. In Styloclieiron, the enlarged 

 third pair has a prehensile form, the terminal segment being, in 

 most cases, opposed to a strong spine or a group of spines on the 

 penultimate segment. In S. abbreviation, G. 0. Sars ( = S. chelifer, 

 Ghun), the spines are replaced by a process of the segment, form- 

 ing a perfect chela. 



The pleopods (Fig. 142, A) are strongly developed in both 

 sexes; the rami are flattened and fringed with long setae; the 

 endopodite has an appendix interna (i) on its inner edge. The 



FIG. 142. 



Abdominal appendages of Meganyctiphanes norvegica (the marginal setae of the rami are 

 omitted). A, pleopod of third pair. B, endopodite of first pair of male, with the copulatory 

 apparatus unfolded. C, telson and uropod. en, endopodite ; ex, exopodite ; i, appendix 

 interna ; s, movable sub-terminal spines of telson ; <, telson. 



first and second pairs are modified as copulatory organs in the 

 male sex, the endopodite having on its inner edge a secondary 

 lobe, which in the first pair (Fig. 142, B) is very large and armed 

 with a complex apparatus of hooks and spines. The uropods 

 (Fig. 142, C) have the exopodite divided by a suture only in 

 Bentheupliamia. 



Internal Anatomy. The details of the internal structure of 

 Euphausiacea are still very imperfectly known. The hepatic caeca 

 appear to resemble those of Decapoda, being generally much rami- 

 fied and forming a large mass lying on each side of the thoracic 

 region. The heart is short, polygonal in outline, with three pairs 

 of ostia. The disposition of the main arterial trunks appears to 

 be similar to that in the lower Decapoda. An antennal gland is 

 present, opening on the proximal segment of the antennal peduncle. 

 In the thoracic portion of the ventral nerve-chain the full number 



