The Entoniscidae pass through a free living Epicaridian and Cryptoniscus stage, and become adult males in the Bopyrus stage. It is stated, however, by Giard and Bonnier[109] that these individuals, which actually function as males, never grow up 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, therefore, 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. [Illustration: FIG. 94.—_Portunion maenadis_, ♀:—=A=, Young, × 10; =B=, older, × 5; =C=, adult, before the eggs are laid, × 3. _A_, 2nd antenna; _Ab_, 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.) ] The Bopyrus fixes in the gill-chamber of the host and becomes converted into the adult female by a series of transformations. As these changes take place it invaginates the wall of the gill-chamber and pushes its way into the thoracic cavity of the crab, though it lies all the time enveloped 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 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 the abdominal segments (_Ab_). In the final stage (C) the incubatory lamellae have further increased in size, and constitute the main bulk of the body; the enormous mass of eggs is passed into the incubatory pouch, and all that remains of the rest of the body is the small head (H) and the abdomen (_Ab_), furnished with its branchiae. Communication with the external world is kept up through an aperture which leads from the brood-pouch into the gill-chamber of the host, and through this aperture the young are hatched out when they are developed sufficiently. The presence of these parasites, although they are never in actual contact with the internal organs of the crab, calls forth the same phenomenon of parasitic castration as was observed in the Rhizocephala. A remarkable association is also found to exist between the Entoniscidae and Rhizocephala, of such a kind that, on the whole, a crab infested with a Rhizocephalan is more likely to harbour an Entoniscid than one without. The explanation of this association is probably that a crab with a _Sacculina_ inside it is prevented from moulting as often as an uninfected crab, and, in consequence, the larval stages of the Entoniscid in the crab’s gill-chamber are more safely passed through. =Sub-Order 7. Phreatoicidea.=[110]