

400 PROVISIONAL HYPOTHESIS Chap. XXVII. 



the male exist, or as with the trimorphic species of Ly thrum 

 and Oxalis, gemmules capable of reproducing several widely- 

 different forms must be latent in each individual. 



The same principle of the latency of certain characters, com- 

 bined with the transposition of organs, may be applied to those 

 singular cases of butterflies and other insects, in which exactly 

 one half or one quarter of the body resembles the male, and the 

 other half or three quarters the female ; and when this occurs 

 the opposite sides of the body, separated from each other by a 

 distinct line, sometimes differ in the most conspicuous manner. 

 Again, these same principles apply to the cases given in the thir- 

 teenth chapter, in which the right and left sides of the body differ 

 to an extraordinary degree, as in the spiral winding of certain 

 shells, and as in the genus Verruca among cirripedes ; for in 

 these cases it is known that either side indifferently may unde 

 the same remarkable change of development. 



Eeversion, in the ordinary sense of the word, comes into action 

 so incessantly, that it evidently forms an essential part of the 

 general law of inheritance. It occurs with beings, however 



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propagated, whether by buds or seminal generation, and some- 

 times may even be observed in the same individual as it advances 

 in age. The tendency to reversion is often induced by a change 

 of conditions, and in the plainest manner by the act of crossing. 

 Crossed forms are generally at first nearly intermediate in cha- 

 racter between their two parents; but in the next generation 

 the offspring generally revert to one or both of their grand- 

 parents, and occasionally to more remote ancestors. How can 

 we account for these facts ? Each organic unit in a hybrid must 

 throw off, according to the doctrine of pangenesis, an abundance 

 of hybridised gemmules, for crossed plants can be readily and 

 largely propagated by buds ; but by the same hypothesis there 

 will likewise be present dormant gemmules derived from both 

 pure parent-forms ; and as these latter retain their normal con- 

 dition, they would, it is probable, be enabled to multiply largely 

 during the lifetime of each hybrid. Consequently the sexual 

 elements of a hybrid will include both pure and hybridised 

 gemmules; and when two hybrids pair, the combination of pure 

 gemmules derived from the one hybrid with the pure gem- 

 mules of the same parts derived from the other would neces- 







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