v ONISCOIDA EPICARIDA 129 



The related Ligidium is found far inland, but always in the 

 neighbourhood of water. These two genera may be distin- 

 guished by the numerous joints in the flagellum of the second 

 antennae, the flagellum being in all cases the portion of the 

 antenna succeeding the long fifth joint. Philoscia tnuscorum 

 occurs usually near the coast, but it is also found inland in 

 England under trees in damp moss. This genus and the 

 common Oniscus, found in woods, are distinguished by the 

 presence of three joints in the flagellum of the second antenna. 

 Philoscia can be distinguished from Oniscus by its narrower 

 body and the pretty marbled appearance of its back. The 

 genus Trichoniscus has four joints in the flagellum ; various 

 species are found in woods. In Porcellio and Armadillidium 

 there are only two joints in the flagellum, while Armadillidium, 

 the common garden wood-louse, can be distinguished from all 

 others by the flattened shape of the uropods, and the habit of 

 rolling up into a ball like an. Armadillo. 



There is also a very peculiar species, Platyarthrus hoffmann- 

 seggii, which occurs in England and Northern Europe, and 

 always lives in ants' nests. It is supposed that they serve as 

 scavengers for the ants, which tend them carefully, and evidently 

 treat them as domestic animals of some kind. The small creature 

 is quite white and blind, and has exceedingly short antennae. 



Sub-Order 6. Epicarida. 



The Epicarida include an immense number of Isopods, parasitic 

 upon other Crustacea. In the adult state they become greatly 

 deformed, and offer very few characters of classificatory value, but 

 they all pass through certain highly characteristic larval stages 

 which are essentially similar in the different families. All the 

 species are protandric hermaphrodites, each individual being male 

 while in a larval state, and then losing its male organisation and 

 becoming female as the parasitic habit is assumed. 



Two series of families are recognised according to the larval 

 stages passed through, the Cryptoniscina, in which the adult 

 male organisation is assumed in the Cryptouiscus stage, and the 

 female condition is imposed directly upon this form, and the 

 Bopyrina, in which the Cryptoniscus passes into a further 

 larval stage, the Bopyrus, which performs the function of the 

 VOL. iv K 



