28 CRUSTACEA BRANCHIOPODA CHAP. 



are not so nearly alike as in most genera of the sub-order, the 

 first two pairs especially having the axis definitely jointed, while 

 the endites are elongated and antenniform ; further, while the 

 first eleven segments bear each a single pair of limbs, as is usual 

 among Crustacea, many of the post-genital segments bear several 

 pairs; thus in Apus cancriformis there are thirty-two post- 

 cephalic segments in front of the telson, the first eleven having 

 each one pair of limbs, while the next seventeen have fifty-two 

 pairs between them, the last four segments having none. 



Tu all the Phyllopoda some of the post-cephalic limbs are 

 modified for reproductive purposes ; in the Branchipodidae the 

 last two pairs (the 12th and 13th generally, the 20th and 21st 

 in Polyartemia) are so modified in both sexes. In the female 

 these appendages fuse at an early period of larval life, and 

 surround the median opening of the generative duct (Fig. 2) ; 

 in the male the two pairs also fuse, but traces of the limbs are 

 left as eversible processes round the paired openings of the vasa 

 deferentia. 



In the other families, one or more limbs of the female are 

 adapted for carrying or supporting the eggs. In the Apodidae 

 the appendages of the eleventh segment have the exopodite in 

 the form of a rounded, watchglass-shaped plate, fitting over a 

 similarly shaped process of the axis of the limb, so that a lens- 

 shaped box is formed, into which the eggs pass from the oviduct. 

 In Limnadiidae the eggs are carried in masses between the body 

 and the carapace, and are kept in position by special elongations of 

 the cxopodites of two or three legs, either those near the middle 

 of the thorax (Estheria, Limnadia), or at its posterior end 

 (Limnetis). In female Limnetis the last thoracic segments bear 

 two remarkable lateral plates, which apparently also help to 

 support the eggs. In the male Limnadiidae, the first (Limnetis} 

 or the first two thoracic feet (Limnadia, Estlieria) are prehensile 

 (Fig. 8, ]i;. 



Alimentary Canal. - - The mouth of the Phyllopoda is 

 overhung by the large labrum, so that a kind of atrium is 

 formed, outside the mouth itself, in which mastication is per- 

 formed ; numerous unicellular glands, opening on the oral face of 

 the labrum. pour their secretion into the atrial chamber, and 

 may be called salivary, though the nature of their secretion is 

 not known. The mouth has commonly two swollen and setose 



