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. These individuals may closely resemble the 

 preceding larval form, but generally are wonderfully dissi- 

 milar. 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 

 remarked, must include gemmules not only of all the succeeding 

 but likewise of all the preceding stages of development; for 

 when mature they have the power of transmitting by sexual 

 generation gemmules of all the stages, however numerous these 

 may be. It was shown in the First Part, at least in regard to 

 animals, that the new beings which are thus at any period 

 asexually generated do not retrograde in development— that 

 is, they do not pass through those earlier stages, through which 

 the fertilised germ of the same animal has to nass: and an 



pass 



explanation of this fact was attempted as far as the final or 

 teleological cause is concerned. We can likewise understand 

 the proximate cause, if we assume, and the assumption is far 

 from improbable, that buds, like chopped-up fragments of a 

 hydra, are formed of tissue which has already passed through 

 several of the earlier stages of development ; for in this case 

 their component cells or units would not unite with the gem- 

 mules derived from the earlier-formed cells, but only with those 

 which came next in the order of development. On the other 

 hand, we must believe that, in the sexual elements, or probably 

 in the female alone, gemmules of certain primordial cells are 

 present ; and these, as soon as their development commences, 

 unite in due succession with the gemmules of every part of 

 the body, from the first to the last period of life. 



The principle of the independent formation of each part, in 



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