OCR Text |
Show 370 CLASSIFICATION. [ORAl'. XIII. the bear genus. The whole case is preposterous ; f?r where there has been close descent in common, there Will certainly be close resemblance or affinity. . . As descent has universally been used .In class1ng to-gether the individuals of the same spec1es, though the l:uales and females and larvre are sometimes extremely different· and as it has been used in classing varieties which h;ve undergone a certain, and sometimes a considerable amount of modification, may not this same element of descent have been unconsciously used in grouping spe- . cies under O'enera, and genera under higher groups, though in these ca~es the modification has been greater in degree, and has taken a longer time to complete ~ I believe it has thus been unconsciously used; and only thus can I understand the several rules and guides which h~ve been followed by our best systematists. We have no written pedigrees; we have to make out community of descent by resemblances of any kind. Therefore we choose those characters which, as far as we can judge, are the least likely to have been modified in relation to the conditions of life to which each species has been recently exposed. Rudimentary structures on this view are as good as, or even sometimes better than, other parts of the organisa- . tion. We care not. how trifling a character may be-let it be the 1nere inflection of the angle of the jaw, the manner in which an insect's wing is folded, whether the skin be covered by hair or feathers-if it prevail throughout many and different species, especially those having very different habits of life, it assumes high value; for we can account for its presence in so many forms with such different habits, only by its inheritance from a common parent. We may err in this respect in regard to single points of structure, but when several characters, let them be ever so trifling, occur together throughout a large group of beings having different habits, we may feel almost sure, on the theory of descent, that these characters have been inherited from a common ancestor. And we know that such correlated or aggregated characters have especial value in classification. We can understand why a species or a group of species CHAP. XIII.] CLASSIFICATION. d t . 371 ~~y epar? In several of its m . IStiCs, from Its allies and yet b osi 1nnportant character- This may be safely done and . e saf e Y classed with them ffi su C.i en t numb er of cha'r act IS o ten done l . 1 , as ong as a portant, betrays the hidden b~~d ~} them be .ever so unimLet two forms have not a sinO'l 1 commu?-Ity of descent. if these extreme forms are co~ e c ;aracter 1n· common, yet of intermediate groups, we m~ec ed toge~her by a chain munity of descent, and we uf tht once 1~fer their comclass. As we find organs of J h he~ all .1nt~ the same -those which serve to preserv~ 1£ ysi~log1cal1mportance conditions of exi~tence-are generealln hr the most diverse we atta.ch especial value to them _Y ~ e ~ost const~nt, organs, In another group or secf 'f ut If these same to differ much, we at once valu 1~h 0 a gr~up, are found cation. We shall hereafter I fu. lem /esslln our classifi-bryological characters are ~f such~· c hal _y ~ee why ~mportance. Geographical distributio;g c assifica~ory 1mbrought usefully into play in cl . ~ay sometimes be distributed ~enera because all ~hs~ng a;ge and widely-genus, inhabiting a~y distinct and isolit~~es of thhe san;e all pwro bability dde scended from th e same parreegnitosn , ave In e can un erstand, on these views th . . tant distinction between real affi . t. ' d e very ~mporadaptive res bl L 111 .1es an analogical or this distincti~~' a~~c~!· has br:~clfyr~~11alle~ batteMntion to and others The r bl . owe Y acleay an: ~n .th~ fin-likee~~~eri~~c~~bs thbe:!:~: tl!'e t~e body b tic ISba pachydermatous anim~l and the whafgon~ e ween oth these mammals d 'fi h . e, an L A_mongst insects ther.e are innu:erab~e e~, ~ analogihcal. mnreus misled b t 1 Ins ances : t us an hom~pterous !n:~terna appearances, actually clas~ed ?f the same kind ev as. a moth. We. see s?mething m the thickened ste en If ohr domestic varieties, as turnip Th ms o t e common and swedj sh is hardly m~:ees;::~ffu~c~hf thfu greyholu~d and ~·acehorse been drawn b an e ana og1es wh1ch have mals. On my s?me authors between very distinct ani-tance for claraill~~~ of chiracters being of real impor- Ion, on y in .so far as they reveal |