On the Variations of certain Crustacea. 327 



ON THE VARIATIONS OF CERTAIN CRUSTACEA, 

 IN RELATION TO THE THEORY OF THE ORIGIN 

 OF SPECIES BY NATURAL MODIFICATION. 



BY GEOEGE S. BEADY, H.E.C.S., C.M.Z.S., 

 Secretary to the Tyneside Naturalists' Field Club. 



Darwin's theory of tlie origin of species has outlived the viru- 

 lent abuse of an extreme school of scientific, or one might 

 more correctly say, of unscientific opinion, and has entered 

 upon a second phase of existence. It has now to undergo 

 the ordeal of a searching comparison with the phenomena of 

 nature ; with phenomena not only old and familiar, but with 

 many others which have been brought to light since the pub- 

 lication of Mr. Darwin's treatise, and with a still greater mul- 

 titude which must before long reward the efforts of such 

 laborious students as are now engaged in the pursuit of natural 

 history. The time must come, though we do not yet see it, 

 in which educated men will be willing to receive new truths of 

 biological science, however much these may conflict with pre- 

 conceived ideas, in a temper as calm as that with which they 

 now contemplate those revelations of geology and astronomy 

 which a past generation counted no better than damnable 

 heresies. 



It is obvious that the lower orders of animals present a 

 field on which the many details of descent and variation can 

 be examined with much greater facility than amongst more 

 highly-organized beings. The great numbers in which mem- 

 bers of many of the lower groups may be obtained, both in a 

 recent and fossil state, their excessive fecundity, their curious 

 metamorphoses, and other circumstances, render it highly 

 probable that amongst them we shall look with the greatest 

 chance of success for information regarding the true relation- 

 ships of species, and the modes in which they have originated. 



There is, doubtless, at the outset, a considerable difficult}'' 

 in accurately defining what we mean by a species. This must, 

 in the long run, be left to the discretion of each observer in 

 the department which he specially cultivates. We can lay 

 down no recognized rule by which one nearly allied species 

 may be absolutely, and without fear of contradiction, sepa- 

 rated from another, and the practice of different naturalists 

 varies in this respect very widely. Thus while " M. Grenier 

 enumerates only twenty-three roses for the whole of France, 

 M. Deseglise describes or mentions one hundred and seven in 

 his elaborate monograph of the French Roses ; and M. Boreau, 

 in the last edition of his Flora, gives seventy-four for the 



