308 



CRUSTACEA. 



parasites are found within tlie body-cavity of the host (crabs, Paguridac), but 

 must be described as ectoparasites, as they are enclosed in a chitinous sat; 

 derived from an invagination of the outer surface of the body (wall of the 

 branchial cavity) of the host. The body of the female (Fig. 148 B) is very 

 peculiar in shape and dorsally curved ; it has a rounded cephalic region {eg) 

 with piercing mouth-parts and vestigies of antennae {ae, ai), an unsegmented 

 thorax {tJi) which carries the ventral brood-cavity formed by the lamellae of 

 the limbs (Fig. 148 A), and a segmented abdomen [ab) with sabre-sliaped or 

 lamellate pleopoda {cn^. The small males (Fig. 147 A) become attached to the 



Ic It JT: 





C 



1 



foC 



Fig. 148.— Adult female of an Entoniscid (PoHunion mnciiadis), after Giard and Bonnier, 

 from Lano's Text-hnok). A, with the brood-cavity jiartly opened in the ventral median line 

 and the brood-lamellae separated. The abdomen (ab) is so placed that tlie ventral side is 

 seen. B, brood-cavity not opened, showing the dorsal surface of the abdomen (ah) I>\ the 

 anterior, middle, and posterior lobes of the first brood-lamella on the right side ; //, the 

 same of the lirst brood-lamella on the left ; //)■, III, second brood lamellae (right and left) ; 

 Illr, nil, third brood-laniellae (right and left); JF, fourth brood-lamella; Vr, VI, fifth 

 brood-lamellae (right and left) ; ah, abdomen ; ae, outer, al, inner antennae ; ex„, exopodite 

 of the second pleopod ; cn^, endopodite of the third pleopod ; ca, cephalic region (so-called 

 cephalogaster) ; h, cardial prominence; mf, maxillipede ; jrf, pleural lamella of the first 

 abdominal segment ; oc, ovary ; tli, thorax. 



females and resemble in appearance the Bopyrid males, being, however, distin- 

 guished from these by the absence of the last pair of thoracic limbs (which 

 have degenerated) and of the second antennae. Tlie young larvae (Fig. 147 B) 

 very closely resemble those of the Bopyridac, and always possess paired eyes 

 {mo), and sometimes also a Nauplius eye {Grapsion). They are distinguished 

 from the Bopyrid larvae chiefly by the shape of tlie penultimate thoracic limbs 

 (f,), which varies in different genera, and also differs from that of the other 



