84 CRUSTACEA. 



the Palinurus is the claw of the lobster in a modified state of 

 develo])ement, or that the former analogically represents the 

 latter ? Should we incur the chance of ridicule if we describe 

 the claw of the lobster as a leg, although it be employed 

 only in prehension, and not in locomotion ? Let us, how- 

 ever, now examine one of the little leaping shrimps, so com- 

 mon on the sea-coast, and of which one species abounds in 

 fresh water {Gammarus pulex), and we find the mouth defi- 

 cient in a certain number of pairs of organs, but that the 

 legs have obtained an increase of the same number of pairs ; 

 whilst the examination of such genera as Sergestes, Sicyonia, 

 &c., clearly demonstrate the transition of structure and func- 

 tion from mouth organs to legs. Will it be said that we are 

 adopting a faulty nomenclature, because we employ a term 

 for these thus altered organs, which indicates that they are 

 liable to this singular kind of transition ? I am aware 

 that, by the unthinking, (and by those who would lead the 

 unthinking by the employment of arguments resting upon 

 general, and, as we may say, vulgar observation, rather than 

 upon accurate but difficult analysis,) we should be ridiculed 

 in asserting that the sucker of the butterfly, and the under- 

 jaws of a beetle, are the same organs in a different state of 

 developement, and in applying to both the same term ; but 

 I contend that the arguments which I have above brought 

 forward are applicable to one case as well as the other ; that 

 there is no fanciful theory to be built upon this strict appli- 

 cation of the rules of analysis and consequent analogies ; 

 and that when, by the application of the former, and the 

 adoption of the latter, we arrive with certainty (and here, as 

 I said in the outset, lies the great difficulty) at the conclu- 

 sion that a certain organ in one animal is the representative 

 of an organ in another animal, we are at liberty, in a strictly 

 philosophic view of the subject, to apply to both the same 

 name, although in common parlance it is necessary, perhaps, 



