YIII PREFACE. 



{Brevoortia tt/nm/ius), in great numl)ers. In namino- l)oth species, the 

 host and the parasite, Latrobe aptly and fancifully considered the case 

 analagous to. that of the ancient chief of state {tyraiiiiw^) and the taster 

 {prxgustator). The parasites of Crustacea infest the shrimps and 

 crabs or decapodous crustacea and the schizopods. When the parasite 

 occupies the branchial cavity of the host, a large protuberance or 

 swelling is apparent on whichever side the body is infested. The 

 parasites are sometimes found in the visceral cavity or even in the 

 incubatory pouch of their hosts. 



The destructive habits of some of the marine and fresh-water species 

 to submerged timber, such as wharfs and bridges, have been hereto- 

 fore recorded," l)ut not until recently has attention been called to the 

 fact that even the terrestrial forms may give cause for alarm in the 

 nature of pests. Several common and well-distributed species have 

 been found menacing young cotton plants, sugar beets, mushrooms, 

 and cucumber vines. 



The burrowing habits of some Isopods are interesting. Chilton says 

 of Scyphax ornatm and AcUvcla euchroa that they "are found on 

 sandy beaches, either on the surface or burying themselves a little in 

 the sand aV)out high water mark or a little lower." Hav, in recently 

 observing the habits of Sci/pJidcdla arejucoJa. Hnds that it also burrows 

 in the sand. The Serolidie, according to Studer, "" live by preference 

 on sandy ground, into which they burrow with their flat bodies up to 

 the caudal plate." 



Whitelegge speaks of the paguroid habits of certain Isopods, which 

 "live in small univalve shells and in company with young hermit 

 crabs." Mimicry of external appearance and similarity of habitat is 

 probably very useful in the struggle for existence. 



Many of the species found in North America also occur in other 

 parts of the world. The terrestrial Isopods have a wide distribution 

 as well as the parasites of fishes. The Arcturida' form a rather 

 restricted group. Benedict says of them, in explanation of this fact, 

 that it is due to structure and habits. "The young are few in a brood 

 and are cared for ))y the parent until well al)le to care for themselves, 

 clinging to the mother's antenna? imtil ready to undertake a more 

 independent existence, perhaps on the ver}' object on which the mother 

 is foraging for hers<>lf and brood. With habits of this kind the 

 chances of a wide distribution for anj- one species must be very umcli 

 less than is the case where free-swijnming young are produced in 

 large numbers." 



I have not attempted to give here a general account of the mor- 

 phology, as the reader is supposed to be familiar with the sources 



«See Charles 11. Snow, Marine Wood-Borers, Trans. Amer. See. Civil luigineers, 

 XL, 1898, pp. i9G-191», for notes in this connection. 



