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. [Illustration: FIG. 90.—_Galathea intermedia_, with a _Pleurocrypta microbranchiata_ under its left branchiostegite (_B_), × 1. (After Sars.) ] [Illustration: FIG. 91.—Ventral view of male _Bopyrus fougerouxi_, × 30. _A_, 1st and 2nd antennae; _T_, 8th (last) thoracic appendage. (After Bonnier.) ] The adult female condition, which is assumed after the Bopyrid stage is passed through, is illustrated in Fig. 92. The body acquires a remarkable asymmetry, due to the unequal pressure exerted by the walls of the gill-chamber. The antennae and mandibles (Fig. 92, B) are entirely covered up by the largely expanded maxillipedes; maxillae are, as usual, entirely absent. Very large lamellae grow out from the bases of the thoracic limbs to form a brood-pouch, and in this manner the adult condition is attained. The final complication in the life-histories of these Isopoda is reached by the family =Entoniscidae=, which are parasitic when adult inside the thoracic cavity of Brachyura and Paguridae. The cephalothorax of a _Carcinus maenas_, which contains an adult _Portunion maenadis_ (_P_), is shown in Fig. 93. The parasite is of a reddish colour when alive. [Illustration: FIG. 92.—_Bopyrus fougerouxi._ =A=, Ventral view of female carrying a male (_M_) between her abdominal appendages, × 8; =B=, ventral view of part of head of female, the maxillipedes and the left mandible having been removed. _A.1_, _A.2_, 1st and 2nd antennae; _M_, male; _Mn_, right mandible; _Mx_, left maxillipede; _O_, oostegite; _T_, left 4th thoracic appendage or 3rd leg. (After Bonnier.) ] [Illustration: FIG. 93.—Cephalothorax of _Carcinus maenas_, seen from the ventral side, containing a parasitic _Portunion maenadis_ (_P_), × ½. (After Bonnier.) ]