40 CRUSTACEA—BRANCHIOPODA CHAP. 
patch (N.m) of columnar ectoderm, containing concretions like 
those described in the Branchipodidae, and behind this is a pair 
of cup-shaped organs (V.e), with raised margins. 
The fold of skin which forms the carapace contains the coils 
of the single pair of kidneys, and it forms an important organ 
of respiration, partly from the great size of the blood-vessels it 
contains, and partly from the presence 
of red, blue, or brown respiratory pig- 
ments in the tissue of the skin itself. 
In most Cladocera the cuticle of the 
carapace is cast at every ecdysis, with 
that of other parts of the body; but in 
Iliocryptus and a few others it remains 
after each moult, giving the carapace 
an appearance of “lines of growth,” 
like that seen in many Limnadiidae. 
The segmentation of the body 
behind the head is obscure, but we 
can generally recognise (1) a thorax, of 
as many segments as there are pairs of 
limbs; (2) an abdomen of three seg- 
ments; and (3) a telson. 
The thoracic limbs of the Calypto- 
ie At Sina eames le mera are flattened, and resemble those 
x 27. Oxford. 4.1, Elon- Of the Phyllopoda; as a type we may 
Bed ot See? ao, examine! (che jauhing thoracic limb of 
organ; N.m, median element Simocephalus (Fig. 12, C), in which 
of dorsal organ ; Te, testes; the axis bears a large setose gnathobase 
3, opening of vas deferens. 5 t=) 
(Gn) on its inner edge, followed by two 
small endites; the terminal process, or exopodite (#), is a large 
flattened plate, with six long plumose hairs on its edge. The 
outer margin of the axis bears a bract (#7) and an epipodite. 
In Simocephalus, as in the other Daphniidae, there are five 
pairs of thoracic limbs, of which the third and fourth are alike ; 
in the female each limb of the first pair consists of a jointed axis, 
with strong biting hairs on the inner border, and a rudimentary 
epipodite (Fig. 12, A), the second limb being more like the 
third, but with a more prominent gnathobase and a narrower 
exopodite (B), while the limbs of the fifth pair have the gnatho- 
base and the exopodite filamentous (D). 
