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 joimted, 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 caneriformis 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. 
Tn 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 exopodites of two or three legs, either those near the middle 
of the thorax (Hstheria, 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 (Zimnetis) 
or the first two thoracic feet (Limnadia, Estheria) are prehensile 
(Fis.<8, B): 
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 
