In the Cryptoniscina the Cryptoniscus larva is the male, and at this stage possesses a pair of large testes in the thorax. The ovaries are also present at this stage as very small bodies applied to the anterior ends of the testes. The larval males in this state seek out adult fixed Danaliae and fertilise them; and, when this is accomplished, they themselves become fixed to the host and begin to develop into the adult female condition. The limbs are all lost, and out of the mouth grows a long proboscis (Fig. [88], P), which penetrates the tissues of the host. The ovaries begin to grow, and a remarkable process of absorption in the testes takes place. These organs, when fixation occurs, are never empty of spermatozoa, and are frequently crammed with them. After fixation some large cells at the interior borders of the testes begin to feed upon the remains of these organs and to grow enormously in size and to multiply by amitosis. These phagocytes, as they really are, attain an enormous size, but they are doomed to degeneration, the chromatin becoming dispersed through the cytoplasm, and the nuclei dividing first by amitosis and then breaking up and disappearing. As the parasite grows, the heart at the posterior end of the body ceases to beat; the ovaries increase enormously at the expense of the alimentary canal, and on the ventral surface two pairs of spermathecae are invaginated ready to receive the spermatozoa of a larval male. In the adult condition, after fertilisation has taken place and the ovaries occupy almost the whole of the body, the remains of the phagocytic cells can be seen on the dorsal surface in a degenerate state. They evidently are not used as food, and their sole function is to make away with the male organisation when it has become useless.[[108]]
Fig. [88].—Side view of Danalia curvata, × 15, shortly after fixation and loss of larval appendages. A, Alimentary canal; E, eye; H, heart; N, phagocytic cells; O, ovary; P, proboscis.
Fig. [89].—Optical section (dorsal view) of Danalia curvata, in the same stage as Fig. [88]. A, Alimentary canal; Ec, ectoderm; H, heart; N, phagocytic cells; O, ovaries; P, proboscis.
In the series Bopyrina, after the free-living Epicaridian and Cryptoniscus stages, a further larval state is assumed, called the Bopyrus, which is the functional male, and, after performing this function, passes on to the adult female condition.
The family Bopyridae is parasitic in the branchial chamber of Decapoda, especially Macrura and Anomura. When one of these Decapods is infested with an adult Bopyrid the gill-chamber in which it is situated is greatly swollen, as shown in Fig. [90]. A very common Bopyrid is Bopyrus fougerouxi, parasitic in the gill-chambers of Palaemon serratus. The Bopyrus larva or functional male has the appearance shown in Fig. [91]. It differs from the Cryptoniscus stage in possessing a rudimentary pair of anterior thoracic limbs and seven pairs normally developed, while the abdominal limbs are plate-like and branchial in function. The male can often be found attached to the female beneath the last pair of incubatory lamellae.
Fig. [90].—Galathea intermedia, with a Pleurocrypta microbranchiata under its left branchiostegite (B), × 1. (After Sars.)
