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Show ON CLASSIFICJATION. nnimal series: tho classification which he adopt cd is a c]assi II cation by organs, and, as suc·h, it is adn1iraoly adapt <l to tho needs of the cmnparative physiologist. But tho student of the geographical distribution of a11imals, regarding anilnated creatures, not as diverse 1nocliGeations of tho great physiological mechanism, but in relat.ion to on0 anot.hor, to plants nnd to telluric concbtions, would, 'nth cqnn1 propncty, dispose of the contents of a Zoological l\f u. eun1 in a totally different manner; basing his classification, not upon organ. , but on distributional assemblages. And the pure pal. ontologi t, looking at life fr01n yet another distinct point of vi w, would associate animalrmnains together on neither of tho. e principles, but would group them according to the order of their succession in Time. Again, that classification whic·h I propose to di ens in tho present Lectures, is different from all of the e : it i meant to snbserve the comprehension and recollection of th facts of anin1al structure; and, as such, it is based upon purely strnctnrnl considerations, and 1nay be designated a 1\Iorphological Classification. I shall have to consirler animals, not ns phy. ioln,o·icnl apparatuses 1nerely; not as related to other forn1. of life and to elimatal conditions; not as successive tenants of tho earth; but as fabrics, each of which is bunt upon n, certain plan. It is possiLle and conceivable thn,t every animal shoul<l hav0 been constructed upon a plan of its own, having no re.·cn1blanro whatsoever to the plan of any other animal. For any reason we can discover to tho contrary, tlw.t combination of nn,tnral forces which we term Life 1night haYe resnltecl fron1, or b0cn mani. fested. by, a series of infinitely diverse structures: nor, indeed, would anything in the nature of the case load ns to suspcc·t a community of organization botweon anilnals Ro different in habit and in. appearance as a porpoise and a gazelle, an oaglo and a crocodile, or a butterfly and a lobst0r. IIad n,nimals Lern thus independently organized, each working out its life by a mechanism peculiar to itself, snch a classifieation as that which is now nnd~r contemplation would obviously be impossible; a mor~holog1ral, or structural, classification plainly implying n1orphological, or structurn,l, re.·mnhlmtcos in the things classified. UTIEOAniNII>A, RHIZOPODA, RPONOIDA, A :rn INFUSORIA. As a 1nattcr of fact, however, no such mutual incl pend -nc of animal forms cxi ts in nature. On the contrary, the different n1emberR of tho ani1nn,l kingdom, fron1 the l1ighc.t to the lowest, aro marvellously interconnoctecL Every aniinal hn,s a something in common with all its follovvs: nn1eh, with many of them ; n1ore, with a few ; mHl, usually, so n1uch with several, that it differs but little from the1n. Now, a 1norphological classiflcntion is a statmnent of those · gradations of Jjkeness which arc obsorvn,blc in anilnal structures ml~ its objects and uses arc 1nanifold. In the first place, i~ stnvcs to throw our knowledge of the fa<'ts which nnclcrlio, and aro tho canso of, tho similarities discerned into tho fewest possible gcn.cral propositions-subordinated to one another, according to ~hou greater or less clegroo of genorn,lity ; and in this wn,y 1t answers the pnrpoRe of a r;nmnoria technica, without which the n1ind would be inco1npetcnt to grasp and retain the multiiarious details of anat01nical science. But thoro is a second and. even mo~·e important aspect of morphological classification. Every group in that classification is such in virtue of certain structural characters, which arc not only common to the 1nmnbcr:::; of that group, hut distinguish it from all others ; ancl the statcn1ent of these constitutes tho definition of the group. Thus, among ani1nals with vertoLrm, the class Mctrnn~;alia is definable as those which have two occipital condyles, with a well-ossified basi-occipital; which have oach ramu. of the mandible c01nposecl of a single piece of bone and n,rticulated with the Rquan1osal clement of the skull; and which possess ma1nmre and non-nucleated red blood-corpuscles. But this staten1ont of the characters of the class JJ[ammah'a i so1nothing more t~an an arbitrary definition. It docs not nwro1y 1ncan that naturalists agree to call such and sueh anin1als Mamr; nalia: hut it expresses, firstly, a gonern,lization based upon, and constantly verified by, very wide experience ; and, seconcll y, a belief arising out of that generalization. ~rho generalization is that, in nature, the structures mentioned ar always found associated together: tho l>eliof' is, that they always have been, and always will h , found so associat d. In other words, the dcfini-ll 2 |
