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Show 390 PROVISIONAL HYPOTHESIS CHAP. XXVII. must suppose that the organs were in fact affected at an earlier age and threw off at this period affected gemmules; but that the affection became visible or injurious only after the prolonged growth of the part in the strict sense of the word. In all the changes of structure which regularly supervene during old age, we see the effects of deteriorated growth, and not of true development. In the so-called process of alternate generation many indi-viduals are generated asexually during very early or later stages of development. rrhese individuals may closely resemble the preceding larval form, but generally are wonderfully dissimilar. To understand this process we must suppose that at a certain stage of development the gemmules are multiplied at an unusual rate, and become aggregated by mutual affinity at many centres of attraction, or buds. These buds, it may be rema~·ked,. must include gemmules not only of all the succeeding but likeWise of all the preceding stages of development ; for when ~ature they have the power of transmitting by sexual generation gemmules of all the stages, however numerous these m~y be. It was shown in the First Part, at least in regard to anrmals, that the new beings which are thus at any period ~sexually generated do not retrograde in development--that 1s, they do not pass through those earlier stao·es throuah which the ferti~ised ger~ of the same animal ha; t~ pass ~ and an explanatwn of this fact was attempted as far as the final or teleological cause is concerned. We can likewise understand the p1:oximate cause, if we assume, and the assumption is far from rmprobable, that .buds, like chopped-up fragments of a hydra, are formed .of tissue which has already passed through sev~ral of the earher stages of development; for in this case then com?onent cells or units would . not unite with the gemmu. les denved from the earlier-form~d cells, but only with those whiCh came next in the order of development. On the other ~and, we must believe that, in the sexual· elements, or probably m the female alone, gemmules of certain primordial cells are pr~sen~ ; and these, ~s soon as t~eir development commences, un1te m due successiOn with the gemmules of every part of the body, from the first to the last p~riod of life. rrhe principle of the independent formation of each part, in CHAP. XXVII. OF PANGENESIS. 391 so far as its development depends on the union of the proper gemmules with certain nascent cells, together with the superabundance of the gemmules derived from both parents and selfmultiplied, throws bght on a widely different group of facts, which on any ordinary view of development appears very strange. I allude to organs which are abnormally multiplied or transposed. Thus gold-fish often have supernumerary fins placed on various parts of their bodies. We have seen that, when the tail of a lizard is broken off, a double tail is sometimes reproduced, and when the foot of the salamander is divided longitudinally, additional digits are occasionally formed. When frogs, toads, &c., are born with their limbs doubled, as sometimes occurs, the doubling, as Gervais remarks,44 cannot be due to the complete fusion of two embryos, with the exception of the limbs, for the larvre are limbless. The same argument is applicable 45 to certain insects produced with multiple legs or antennre, for these are metamorphosed from apodal or antennreless larvre. Alphonse Milne-Edwards 46 has described the curious case of a crustacean in which one eye-peduncle supported, instead of a complete eye, only an imperfect cornea, out of the centre of which a portion of an antenna was dev~loped. A case has been recorded 47 of a man who had during both dentitions a double tooth in place of the left second incisor, and he inherited this peculiarity from his paternal grandfather. Several cases are known 48 of additional teeth having been developed in the palate, more especially with horses, and in the orbit of the eye. Certain breeds of sheep bear a whole crowd of horns on their foreheads. Hairs· occasionally appear in strange situations, as within the ears of the Siamese haity family; and hairs "quite natural in structure" have been observed "within the substance of the brain." 49 . As many as five spurs have been seen on both legs in certain Game-fowls. In the Polish fowl the male is ornamented with a topknot of hackles 44 'Compte Rendu,' Nov. 14, 1864, p. 800. 43 As previously remarked by Quatrefages, in his 'Metamorphoses de !'Homme,' &c., 1862, p. 129. 46 Giiuther's 'ZoologicAl Record,' 1864, p. 279. 47 Sedgwick, in 'Medico-Chirurg. Review,' April1863, p. 454. 4s Isid. Geoffroy St. Hilaire, 'Hist. des Anomalies,' tom. i., 1832, pp. 435, 657 ; and tom. ii. p. 560. 49 Virclww, ' Cellular Patholo(Ty' 1860, p. 66. 0 ' |