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 P 



take place it invaginates the wall of Pig. 93.— Cephalothorax of Ca?- 



, -n 1 1 ^ 1 - . cinus maenas, seen from the 



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



into the thoracic cavity of the crab, parasitic Pm-tunion maen- 



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 Pig. 94. The 



Fig. 94.— PorfM-ftiore maenadis, 9 :— 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 ; B', its lateral lobe ; //, 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 



