ISOPODA. 



487 



mouth by means of which it buries its anterior portion, which becomes 



elongated, in the body of the Cirripede (Fig. 302) and thus absorbs the 



nourishment derived (in the case of the Rhizo- 



cephala) from the body of the crab or hermit f> 



crab on which in its turn the host is parasitic 



(Fig. 277, p. 430). 



The dilated intestine ends blindly. The heart 

 and ovary persist at the posterior end of the 

 retort-shaped body, but the heart may disappear 

 in the course of further growth. The eggs de- 

 velop within the body of the mother, and escape 

 by the bursting of the body wall. 



The Entoniscidae go through a similar meta- 

 morphosis, the young in the male phase being 

 attached to the bodies of the " females," as in 

 the Bopyridae, but themselves afterwards pass- 

 ing into the female phase (see p. 491). A second 

 form of male individual is, however, in the 

 Entoniscidae, found on the " females," and 

 these are regarded by Giard and Bonnier as 

 "male" larvae which have for some reason 

 failed to effect their further metamorphosis. So 

 that we appear to have in this sub-family a case of 

 sexual dimorphism in which as in some Cirripedes 

 hermaphrodites and dwarf males occur, but 

 here the phenomenon is complicated by the 

 hermaphrodites being protandrous. 



Section 1. ISOPODA GENUINA. 



---mu 



The second thoracic segment distinct 

 from the cephalo-thorax, the eighth nor- 

 mally developed and bearing limbs. Seven 

 thoracic limbs always present in the 

 young, after the larval stage. 



ov 



FIG. 302. Young female of 

 Cryptoniscus paguri (after 

 Frai?se). an anus (im- 

 pervious) ; c heart ; in 

 intestine ; mu muscles ; o 

 mouth; oe oesophagus ; ov 

 ovary ; pa papillae about 

 the mouth ; s skin of 

 the Cirripede host. 



Tribe 1. ONISCOIDEA. 



Woodlice. Body oval. First antennae vesti- 

 gial. Mandibles without palps. Abdominal feet adapted for air breath- 

 ing, the endopodites form delicate branchiae, the exopodites constituting 

 horny opercula, which in the case of the two anterior feet in Porcellio and 

 Armadillium contain air-chambers. Terrestrial. 



Fam. 1. Oniscidae. Ligia Fab. ; Titanethes Schiodte : Ligidium 

 Brandt ; Styloniscus Dana ; Trichoniscus Brandt ; Philoscia Latr. ; Deto 

 Guer ; Oniscus Linn. ; Porcellio Latr. (Fig. 297) ; Cylisticus Schnitzl. ; 

 Platyarthrus Brandt ; Armadillidium Brandt ; Pseudarmadillo Sauss. ; 

 Sphaeroniscus Gerst. ; Periscyphis Gerst. ; Armadillo Latr. ; Tylos 

 Aud. ; Syspastus Budde-Lund. 



Tribe 2. ASELLOTA. 



Some abdominal legs adapted for respiration in water and generally 

 covered by the first, which form an opercular plate. Uropods terminal. 



