176 



THE CRUSTACEA 



Fig. 100. 



Second thoracic appendage of irnntliophfius 

 longispina. br, branchia ; ej), epipoilial proct-s: 

 ex, exopodite. (After Sars.) 



gastridae and Eucopiidae are attached to the body-wall or to the 

 articular membrane rather than to the coxopodites of the limbs, it 

 is probable that they are really of the nature of epipodites. In 



Gnafhojjhausia a short finger-like 

 process bearing long setae is 

 found on the outer side of the 

 coxopodite, and apparently re*^ 

 presents a reduced distal epi- 

 podite (Fig. 106, cp). In the 

 Mysidae and Petalophthalmidae 

 there are no epipodites on the 

 limbs posterior to the first 

 thoracic pair, apart from some 

 vestiges described in Euchae- 

 iomera and allied genera. Seven 

 pairs of oosfegifes are found 

 attached to the coxopodites of 

 all except the first pair of 

 thoracic appendages in the 

 females of the Lophogastridae, 

 Eucopiidae, and Petalophthal- 

 midae, and in the genus Boreo- 

 myds among the Mysidae. In the other Mysidae the number does 

 not exceed three pairs, and it is often reduced to two, corre- 

 sponding to the last two thoracic somites (Fig. 101, 0). 



The lAeapods are well developed in both sexes in the Lopho- 

 gastridae and Eucopiidae, where they have multiarticulate rami 

 fringed with setae, and no special modifications are found in either 

 sex. In the Petalophthalmidae and Mysidae the pleopods are 

 vestigial in the female (except in the little-known Archaeomysis), 

 but are often well developed in the male. When they are reduced 

 in the latter sex some of the pairs, most commonly the fourth, are 

 specially modified. In the males of some Mysidae the peduncle 

 bears distally, in addition to the two rami, a lobe or process of 

 varying form, to which a branchial function has been attributed. 



The tiropods have the exopodite divided into two segments by 

 a transverse suture in the Lophogastridae, Eucopiidae, and Petaloph- 

 thalmidae, and, less distinctly, in certain Mysidae. A statocyst is 

 present near the base of the endopodite in most ]\Iysidae, but it 

 is absent or vestigial in Boreomysis and in the other families. 



Alimentary System. — The stomach in Mysis (Fig. 107, st) is 

 divided into a globular cardiac portion occupying the greater part 

 of the cavity of the head in front of the cervical sulcus and a much 

 smaller pyloric portion. The interior of both chambers has 

 numerous ridges and prominences armed with spines and setae. 

 In particular, a tongue-shaped process directed backwards on the 



