STRUCTURE OF THE CRUSTACEA. 387 



and Anoplura: and are all hexapods, the former are 

 covered with hair or scales, and the tail has filaments 

 or setae whereby they jump ; they are very active,, and 

 occur in neglected collections or among rejectamenta and 

 refuse. They comprise Lepisma, Forbicina, Podura, 

 &c. ; in the latter, the forked tail is hent beneath the 

 abdomen, and forms a leaping apparatus. The Ano- 

 plura consist of the lice, which are all parasites, some 

 one being peculiar to all animals and birds ; and one, in 

 particular, is the cause of a disgusting disease, the Phthi- 

 riasis, instances of which now rarely occur, but which 

 was comparatively common during the middle ages. 



(351.) The fourth division of the Aptera, the CRUS- 

 TACEA, is allied to the Myriapoda by means of Oniscus; 

 but here again, in this order, we shall reverse the affi- 

 nities, and proceed in a declining line from the superior 

 to the inferior. The subject of a metamorphosis we 

 have before noticed, in speaking of Mr. Thompson's 

 researches, and shall not resume it here, farther than by 

 observing that it has very recently been confirmed by 

 Rathke.* In speaking of the order generally, we may 

 observe, that although they possess symmetrical forms, 

 yet is it combined with such eccentric extravagance as 

 to outrage all preconceived notions of elegance and 

 beauty. How it was that many of them were ever se- 

 lected as choice comestibles, we know not; and it must 

 certainly be considered a vagary of human caprice, 

 which can sit down with zest to a lobster or crab salad, 

 that would turn with disgust from a stew of caterpillars, 

 although the latter are by far the most cleanly feeders. Did 

 the public appetite take this turn, we should not then 

 vainly ask for remedies against the destroyers of our crops, 

 but which would thus yield us other crops equally ser- 

 viceable and beneficial ! This division combines structural 

 differences and peculiarities far more varied than we ob- 

 served in the Arachnidce, but which we must treat more 

 briefly, for our space precludes the amplitude of detail that 

 can alone make such particulars instructive or amusing ; 



* Wiegman's Archiv., part iii. 1840. 

 C C 2 



