162 



KNOWLEDGE. 



[July 2, 1900. 



smaller, aud the need for them larger, every yeai-, a fact 

 which has given rise to disquieting prophecies of coming 

 Nitrogeu-stai-vation and the consequent failure of the 

 world's sujjply of wheat.|t 



THE KARKINOKOSM, OR WORLD OF 

 CRUSTACEA. 



By the Rev. Thomas R. R. Stebbing, m.a., f.r.s., f.l.s., 

 F.Z.S., Author of "A History of Crustacea," " T/ie 

 Naturalist of Cumbrae," " Beport on the Amphipodu 

 collected by H.M.S. ' Challemjer,' " etc. 



FISH-BEARS AND THEIR KINDRED. 

 Emerson was extremely worried by Carlyle's reiterated 

 use of the fantastic expression " gigmanity." Chry- 

 sostom's congregation grew tired of his orations against 

 swearing, even while they continued to swear. The per- 

 severing student may weary of being told that a wood- 

 louse is a crustacean, before he has become conscientiously 

 convinced that it is one. The old writers were far from 

 accepting the fact. They pertinaciously kept the 

 members of the group apart, under names which to this 

 day have not been discarded, though employed now in a 

 very restricted application, these names being the Greek 

 Oniscus, a little donkey, and the Latin Asellus, which 

 likewise means a little ass. This asinine herd, however, 

 included and excluded many creatures which should have 

 been respectively outside it and within. The woodlouse 

 may be taken as a sort of exemplar or figure-head, to 

 introduce and typify the enormous, diversified, world- 

 wandering order of the Isopoda. The name, meaning 

 equal-footed or like-footed, was coined by Latreille, with 

 a view not to the whole of the order as it is now known, 

 but to a limited number of familiar species, which really 

 have the character implied in the designation. In truth, 

 there are to be found in this, as in many other orders 

 of Crustacea, combinations of feet which exhibit no 

 monotony of shape, and are almost grotesque in in- 

 equality of size. 



The retention of the name, in spite of its being not 

 completely applicable, is a matter of convenience, just 

 as human families retain names such as Webster and 

 Talboys, when their members in general have ceased 

 from weaving the waqD and the woof, or from shaping 

 the timber of the forest. Peers and popes and places 

 on a map ai-e allowed to confuse their identity by an 

 unregulated change of name, but science is opposed to 

 such a proceeding. A name is not a definition, and 

 when lawfully given it is not to be lightly altered even 

 on pretence of improvement. The application may be 

 expanded or contracted, just as Rome and Romney may 

 pass through alternations of little and large without 

 ceasing to be Rome and Romney. The Isopoda began 

 with a few genera and species, which during this century 

 have been multiplied into a great horde. Of this number 

 it must be acknowledged that some are separated from 

 the rest by rather trenchant differences. There is a 

 group in which the heart and breathing apparatus are 

 near the head instead of in the caudal region. To these 

 perhaps we ought to apply a name invented by Dana, 

 Anisopoda, which simply means Notlsopoda. There 

 is an objection to negative names on the ground of their 

 indefiniteness. In this case, for instance, it may be 

 alleged that, apart from the Isopoda, everything in 

 heaven and earth is " Notran-Isopod." That is true, 

 yet such a word as Anisopoda serves, better than the 



XX Su' Will. Crookes. Presidential Address to the British Asso- 

 ciatiou. Brijlul, 1898. " The Wheat Problem." Loudon, 1899. 



more recently proposed Tanaidacea, to remind us that 

 the objects so named were once upon a time regarded 

 as Isopoda, and that they have at least some superficial 

 characters in common with that order. 



Leptoehelia forresii, Stebbing. Feet of right side omitted. 



Elaboi'ate details of the structure cannot be given here, 

 but a representation is offered of a species from the 

 family Tanaidse, without prejudice to the question 

 whether this family, and its companion, the Apseudidae, 

 should be counted as belonging to the order Tanaidacea, 

 the section Anisojsoda, or the tribe of the Isopoda cheli- 

 fera. The species figured, Leptoehelia Forresti, is found in 

 the West Indies. The enormous claws signalise its 

 masculine sex. They need not inspire alarm, as they are 

 attached to a body only a quarter of an inch long, with 

 jaws as gentle as those of any " sucking-dove." 



Passing on, then, to the section of the Euisopoda, that 

 is, the good, the orthodox, the genuine Isopoda, which 

 are accepted always, everywhere, and by everybody, we 

 find a further sub-division into tribes, which may have 

 unforeseen consequences in the future. The natural man 

 is distinguished from the naturalist in this way. The 

 natural man, having with pains and reluctance got into 

 his head a scheme of classification for some group of 

 objects, wishes to have that scheme permanent and un- 

 alterable. The naturalist, on the other hand, is aware that 

 fixity of classification means stagnation of enquiry. The 

 more objects he knows about and the more he knows about 

 the objects, the less possible does it continually become for 

 him to fit the new facts into the old framework. Hence 

 come re-arrangement, the disruption of old ties, the 

 formation of fresh alliances, and science which, as above 

 explained, is so jealous to preserve the established names 

 of things, must still be fertile in new terms to express 

 their newly discovered relationships. 



Of the land isopods, embraced at present in the tribe 

 Ouiscoida, mention has been made in earlier essays 

 (Knowledge, Vol. XXL, p. 106, Vol. XXIL, p. 285). The 

 insularity of our island is emphasized by the fact that 

 as yet only nineteen species of this group are known in 

 England, Wales, and Scotland. Ireland has a still 

 smaller number, but includes therein the active 

 Trichonisus vividus (Koch), not recorded from any 

 British locality on this side of the Irish Channel. In 

 other j'aits of the world the species are very numerous, 



