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Show I 164: JJ.AR WINIAN A. tinction not shared by genera and oth.er groups which were no t supp osed to be genealogicadlilfy cohn' nec·t ed. H ow a d en.· vat ive hypothesis would mo yfi t . 1s V. Iewb, in ass.1 gn.m g to species only a temporary xity., IS o - . y t 'f naturalists adopt that hypothesis, they VlOUS. e , I • • h' h l will still retain J ussieu's definitiOn, w IC e~,ves ~n-touched the question as to how and when the. pmennial successions" were established. The practical ques- tw. n w1· n on1 y be, How much difference betwee.n .tw o sets of individuals entitles the~ to rank ~nder distmct • 11 and that is the practical questiOn now, on species~ . . whatever theory. The theoreHcal questiOn Is-as stated at the beginning of this article-whether these spee1'f ie lines were always as distinct as n·o w. f · Mr. Agassiz has "lost no opportum~y o .urgmg the idea that, while species have no ma.tenal existence, they yet exist as categories of thought In t~~ same way [and only in the same way J as genera, families, orders, classes," etc. He "h s taken the ground that all the natural divisions in t.he ani-. 1a k'ngdom are pn.m an·l y d'I S tm' et ' .!iO' Un ded upon d1fferent :~e o:·ies of characters, and that all exist. in. th.e .same '!"~y, that~ I S as cat egorJ. es of thought ' embodied m md1.v 1dbu al hv. mg1 forms.' I have attempted to show that branches m t e amma kingdom are founded upon different plans of .str~cture, .and for that very reason have embraced from the begmnmg repies~n~atives between which there could be no community of o.ngmf; that classes are founded upon d'1:i lle rent modes of executtw tn' o these Plans and therefore they also embrace represen a Iv.es which could' ha\e no community of on· g·m ; th a t orders rep1 e- sent the different degrees of comp 1w' a t1' 0D m· the mode. of exebcicuhtion of each class and therefore embrace representativebs w - ' . f · · more than t e mem could not have a community o origm ~ny . . are founded bers of different classes or branches i that families JJAR WIN ANJJ HIS REVIEWERS. 165 upon different patterns of form, and embrace representatives equally independent in their origin; tLat genera are founded upon ultimate peculiarities of structure, embracing representatives which, from the very nature of their peculiarities, could have no community of origin; and that, finally, species are based upon relations and proportions that exclude, as mnch as all the preceding distinctions, the idea of a common descent. "As the community of characters among the beings belonging to these different categories arises from the intellectual connection which shows them to be categories of thought, they cannot be the result of a gradual material differentiation of the objects themselves. The argument on which these views are founded may b~ summed up in the following few words: Species, genera, families, etc., exist as thoughts, individuals as facts." 1 An ingenious dilemma caps the argument : "It seems to me that there is much confusion of ideas in the general statement of the variability of species so often repeated lately. If species do not exist at all, as the supporters of the transmutation theory maintain, how can they vary? and if individuals alone exist, how can the differences which may be observed among them prove the variability of species? " Now, we imagine that Mr. Darwin need not be dangerously gored by either horn of this curious dilemma. Although we ourselves cherish old-fashioned prejudices in favor of the probable permanence, and therefore of a more stable objective ground of species, yet we agree-and Mr. Darwin will agree fully with Mr. Agassiz-that species, and he will add varieties, "exist as categories of thought," that is, as cognizable distinctions-which is all that we can make of the phrase here, whatever it may mean in the Aristotelian metaphysics. Admitting that species are only cate- 1 In American Journal of Science, July, 1860, p. 143. 8 |
