VIII 



ARTHROPODA 



219 



and under lips, and which become parasitic on other Crustacea. 

 The shapes of some of these parasitic forms have become distorted 

 out of all recognition, especially in the female sex. In Portunion 

 (Fig. lG8),for instance, which belongs to the family of the Entoniscidae, 

 the " oostegites " of the thoracic legs become enlarged into long leaf- 

 like folds which are packed together like the leaves in a bud, the 

 legs themselves having completely disappeared. The head, with its 

 sucking apparatus, forms a small rounded knob, whilst the abdomen 



B 



\ 



Fit;. 167. Larva and adult female of Pnrtiiiiio/i macnadis. (After Giard.) 



A, larva, dorsal view. B, adult female, lab-nil view, abd, abdomen; afl, aiitennule ; "/-, antenna ; 

 In; brood-sac composed of conjoined ovigerous plates of thorax; g, jaws or gnatliib's ; li, lirad ; //, 

 swimmerets or pli-opods. 



is bent back over (not under) the thorax, and its appendages take 

 the form of crimped laminae. 



The larvae of these extraordinary forms have the depressed body 

 and segmentation of a normal Isopod (Fig. 16*7) : a short pair of first 

 and a long pair of second antennae, and six pairs of unforked 

 thoracic legs followed by six pairs of forked abdominal ones. The 

 jaws are already lancet-like and the lips united. In all but these 

 last two points they resemble the young of normal Isopoda when 

 they leave the brood-pouch, and not even the most determined 



