40 



CRUSTACEA — BRANCHIOPODA 



patch (aV./n) of columnar ectoderm, containing concretions like 

 those described in the Branchipodidae, and behind this is a pair 

 of cup-shaped organs {N.e), with raised margins. 



The fold of skin which forms the carapace contains the coils 

 of tlie 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 

 lliocryptus 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- 

 ^ ,, ,,., „. , mera are flattened, and resemble those 



Fig. 11. — Sida crystallma, male, 



X -27. Oxford, .i.i, Eion- of the Phyllopoda ; as a type we may 

 gated first antenna ; i\^.c examine the third thoracic limb of 



paired element of dorsal 



organ; ^A': TO, median element SimOcejjJialuS (Fig. 12, C), in whicll 



. l",S'S";s^£:S ' the axis bears a large setose gnathobase 



(Gn) on its inner edge, followed by two 

 small endites ; the terminal process, or exopodite (Ux), is a large 

 flattened plate, with six long plumose hairs on its edge. The 

 outer margin of the axis bears a bract (Br) and an epipodite. 



In Simocephalus, as in the other Daphniidao, 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 liairs 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 tlie limbs of the fifth pair have the gnatho- 

 base and the exopodite filamentous (D). 



