Vv EPICARIDA——LIFE-HISTORY OF ENTONISCIDAE 135 
into adult females, though all the adult females have passed 
through 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 these changes 
take place it invaginates the wall of Fic. 93.—Cephalothorax of Car- 
Z ‘ cinus maenas, seen from the 
the gill-chamber and pushes its way ventral side, containing a 
into the thoracic cavity of the crab, parasitic Portunion muaen- 
: : 2 Gis (UP) xe ak (After 
though it lies all the time enveloped — Bonnier.) 
in the invaginated wall of the gill- 
chamber, and not free in the body-cavity of the crab. The 
transformations which it undergoes are shown in Fig. 94. The 
Fic. 94.—Portunion maenadis, 9:—A, Young, x 10; B. older, x 5; C, adult, 
before the eggs are laid, x 3. A, 2nd antenna; Ad, abdomen; B, anterior lobe 
of brood-pouch ; B’, its lateral lobe; H, head; 1, 2, 1st and 2nd incubatory 
lamellae (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 
