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Show 372 PROVISIONAL IIYPOTIIESTS C IIAP. XXVII. mental endowments and Lodily powers are all inherite(l. N otbing in the whole circuit of physiology is more wonderful. ~{ow can the use or disuse of a particular limb or of ~he b~·am affect a small aQ"greO'ate of reprodnC"tive cells, seated m a drstant part < ,..., l 1. • o· d lolled from of the body, in such a manner that t 1e u eJ~ ;-, eve these cells inherits the characters of mt~1er one. or both parents? Even an imperfect n.nswer to this question would be sati sfactory. . • c1 t t" lly differ as we 11 n.ve Sexun.l reproductiOn oes no essen Ia ' ~ f b dd" (j or self division ano these proeesses graduate seen, r om u m.o . . - . . ' . . . l lo rnent and throuo·h the reparr of I11JUl"Ies mto ordtnai Y c eve P growth; it might therefore b~ expeeted that every ehara,ct.er would be as regnlarly transm1tterl by all the methods ot Ieproduction as by continued growth. I.n the chn.pters dev~t.ed to inheritance it was shown that a mn1tttncle of newly-acqun ed characters, whether injurious or beneficial, whether of the lo.west or highest vital importance, are often faithfu1ly transmitted -frequently even when one parent alone possesses some new peculiarity. It deserves especial attention that charae.ters appearing at any age tend to reappea:· at a corre~pond~n g ag~. vVe may on the whole conelude that m all cases mh er~tance IS the rule, and non-inh eritn.nce the anomaly. In some mstances a character is not inherited, from the conditions of life being directly opposed to its development; in many. in.si.ances, fr~m the conditions incessantly indncing fresh vanaL1hty, as With <nafted fruit-trees and highly cultivated flow ers. In the re~ aining cases the failure may be attributed to reversion, by whieh the child resembles its grandparents or more remote progenitors, instead of its parents. This principle of Reversion is the most wonderful of a~l ~be attributes of Inheritance. It proves to us that the transm1sswn of a character and its development, whi ch ordinarily go together and thus eseape di scrimination, are di stinct powers ; and these powers in some cases are even antagoni:;;tic, for each acts alt-ernatPly in successive generations. Reversion is not a rare event, depending on some unusual or favoura1le combination of circumstances, but occurs so regularly with crossed animals ancl plant s, and so frequently with uncrossed breeds, th a~ it is evidently an rssential part of the principle of inheritance. vr e know that CHAP. XXV!l. OF' PANGENESIS. 373 changed conditions have the power of evoking long-lost characters, as in the ca~:;e of some feral animals. The ad of crossing in itsnlf possesses this power in a high degree. \Vhat can be more wonderful t ltan tb u.t characters, whi ch ltave disappeared during scores, or hn ndrec.ls, or even thousands of generations, should suddenly reappear perfectly developed, as in the case of pigeons aucl fowls when purely 1red, and especially wh8n crossed ; or as with the zebrine stripes on dun-coloured horses, and oth er such cases ? .!Hany monstrosities come under this same head, as when rndimentary organs are redeveloped, or when an organ which we mnst believe was possessed by an <'.:arly progenitor, but of which not even a rudiment is left, suddenly reappears, as with the fifth stamen in some Scrophulariacem. \Ve have already seen that reversion acts in budreproduction; and we know tb at it occasioually ac:ts during the growth of the same individual animal, especially, but not exclusively, when of crossed parentao·e,-as in the rare cases described of i~dividual fowls, pigeons, 0 cattle, and rabLits, which ltave reverted as they advanced in years to the colours of one of their parents or ancestors. vV e are led to believe, as formerly explained, that every charact er which occasionally reappears is present in a lat ent form in each generat ion, in nearly the same manner as in male and female animals secondary characters of the opposite sex lie latent, ready to be evolved when the reproductive organs are injured. This comparison of the secondary sexnal characters which are latent in both sexes, with other latent characters, is the more appropriate from the case recorded of the Hen, which assumed some of the masculine charact ers, not of her own race, but of an early progenitor; she thus exhibited at the same time the redevelopment of latent characters of both kinds and connected both classes. In every living creature we may feel assured that a host of lost characters lie ready to be evolved under proper conditions. How can we make int elligible, and conneet with other facts, this wonderful and common capacity of reversion,-this power of calling back to life long-lost characters? |
