EPICARIDA LIFE-HISTORY OF ENTONISCIDAE 



135 



into rtdult feiimles, though all the adult females have passed 

 througli a male stage in which the male genital ducts are not 

 formed. The hermaphroditism, there- 

 fore, in these animals at any rate is 

 absolutely useless from a reproductive 

 point of view, and this justifies our 

 looking for some other explanation of 

 it, such as was suggested on p. 105. 



The Bopyrus fixes in the gill- 

 chamber of the host and becomes con- 

 verted into the adult female by a series 

 of transformations. As tliese changes P 



take place it invaginates the wall of Fig. 93.— Cephalothoraxof Ca»- 



, , -111 1 1 1 -i cinus maenas, seen from the 



the gill- chamber and pushes its way central side, containing a 



parasitic Portunion maen- 



adis (P), 

 Bonnier. ) 



into the thoracic cavity of the crab, 

 though it lies all the time enveloped 

 ill the invaginatecl wall of the gill- 

 chamber, and not free in the body-cavity of the crab, 

 transformations which it undergoes are shown in Fi" 94. 



(After 



The 



The 



Fig. 94. — Portunion viaenadis, ? : — A. Young, x 10 ; B. older, x 5 ; C, adult, 

 before the eggs are laid, x 3. A, 2nd antenna ; Ab, abdomen ; B, anterior lobe 

 of brood-pouch ; />", its lateral lobe ; //, head ; 1, 2, 1st and 2nd incubatory 

 laniellae (oostegites). (After Giard and Bonnier.) 



body first assumes a grub-like appearance (A), and two pairs of 

 incubatory lamellae (1, 2) grow out from the first and second 

 thoracic segments. In the next stage (B) these lamellae assume 

 gigantic proportions, and four pairs of branchiae grow out from 



