ISOPODA. 491 



C. balani (Bate) in the mouth space of Balanus balanoides ; Leponiscus 

 Giard, L. pollicipedis . 



Fam. 7. Entoniscidae. The females (Fig. 303) when fully grown are 

 markedly deformed, the abdomen being bent dorsally, 2-3 cm. in length, 

 and enclosed within the bodies of Brachyura and Anomura, which they 

 enter as larvae from the branchial cavity, the hypodermis of the host 

 being invaginated and forming an envelope for the parasite. The aperture 

 of invagination remains open as a respiratory passage. Brood lamellae 

 large, lobed ; thoracic feet vestigial ; abdominal feet branchial. Two 

 kinds of males with ripe testes, both very minute, are found about the 

 female : one active '3 mm. long with well developed appendages ; the 

 other 1 mm. long somewhat degenerate and torpid. From the presence 

 of vesicles containing spermatozoa on the last thoracic segment of the 

 young female, and of the remains of testes (?), it is supposed, as in the 

 case of the last family, that the animals are hermaphrodite and pro- 

 tandrous, being at first male, and subsequently acquiring the female 

 form. The males of the second kind have, it is supposed, failed to effect 

 this transformation and remain permanently male. Entoniscus Fr. Mull, 

 on Porcellana ; Entione Kossm. on Achaeus. Grapsion G. and B. on 

 Pachygrapsus ; Cancrion G. and B. and Portunion G. and B., spp. on 

 various Brachyura. P. maenadis abundant on Carcinus maenas Penn. 

 (" on 1 in 100 "). 



Fam. 8. Bopyridae. Parasitic in the branchial cavity or elsewhere 

 about the body of Decapod Crustacea. Sexual dimorphism very marked. 

 Female large, flattened, usually unsymmetrical, blind and with vestigial 

 antennae, mandibles styliform and other mouth parts much reduced. 

 Thoracic feet (6-7) short and hooked, abdominal may be absent, or (lone 

 and its allies) long, branched and filiform. The dwarf males are sym- 

 metrical, long in proportion to their breadth (Fig. 299) and retain their 

 yes. Phryxus Ratbke ; Athelgue Hesse ( = Athelgus and Athelges) on 

 Pagurids ; Pleurocrypta Hesse, on Porcellana and Galathea. Palaegyge 

 G. and B. on Caridea, Pseudione Kossm. and Gyge Cornalia and Panceri 

 on the Anomura (Fig. 299) ; Kepon ( = Cepon) Duvernoyon a crab; Leidya 

 Cornalia and Panceri, on Gelasimus ; Grapsicepon G. and B. ; Cancricepon 

 G. and B. and Ergyne Risso ( = Portunicepon Kossm.) on Brachyura; 

 Gigantione Kossm. ; lone Lat. on Thalassinidea ; Argeia Dana, Bopyrus 

 Lat. (Fig. 300), Probopyrus G. and H.,Bopyrina Kossm., Bopyroides Stimpson 

 and Hemiarthrus G. and B. on Caridea. Phyllodurus Stimpson on Upogebia. 



Section 2. ISOPODA ANOMALA.* 



The second thoracic segment (the first free segment in other 

 Isopods) fused with the head, the eighth reduced and without 

 appendages. There are onty five ambulatory limbs. 



Fam. Gnathiidae. Aberrant Isopods which undergo a remarkable 

 metamorphosis. The young, apparently until the last moult, though 



* Dohrn, A., Unters. lib Bau und Entwick. der Arthropoda, 4. Entwick. 

 und Organ, von Praniza (Anceus) maxillaris, Zeits. /. wiss. Zool. vol. 20 

 {1870), p. 53. See als^o Hesse, Mem sur les Praniza et les Ancees, Ann. des 

 Sc. Nat. Ser. 4, 9 and Ser. 5, 19. Sp. Bate and Westwood, Brit. Sessile- 

 Eyed Crustacea, and G. O. Sars, Crustacea of Norway, Isopoda, p. 50. 



The Gnathiidae are included by Sars in the Tribe Flabellifera. 



