Chap. XXVII. OP PANGENESIS. 393 



under domestication, when we remember the many curious 

 cases given, in the seventeenth chapter, of cultivated plants 

 which absolutely refuse to be fertilised by their own pollen 

 or by that of the same species, but are abundantly fertile 

 with pollen of a distinct species ; for this implies that their 

 sexual elective affinities — and this is the term used by Gartner 

 — have been modified. As the cells of adjoining or homologous 

 parts will have nearly the same nature, they will be liable to 

 acquire by variation each other's elective affinities ; and we can 

 thus to a certain extent understand such cases as a crowd of 

 horns on the heads in certain sheep, of several spurs on the leg, 

 and. of hackles on the head of the fowl, and with the pigeon the 

 occurrence of wing-feathers on their legs and of membrane 

 between their toes ; for the leg is the homologue of the wing. 

 As all the organs of plants are homologous and spring from a 

 common axis, it is natural that they should be eminently liable to 

 transposition. It ought to be observed that when any compound 

 part, such as an additional limb or an antenna, springs from a 

 false position, it is only necessary that the few first gemmules 

 should be wrongly attached ; for these whilst developing would 

 attract others in due succession, as in the regrowth of an 

 amputated limb. When parts which are homologous and 

 similar in structure, as the vertebras in snakes or the stamens 

 in polyandrous flowers, &c, are repeated many times in the 

 same organism, closely allied gemmules must be extremely 

 numerous, as well as the points to which they ought to become 

 united; and, in accordance with the foregoing views, we can 

 to a certain extent understand Isid. Geoffroy St. Hilaire's law, 

 namely, that parts, which are already multiple, are extremely 

 liable to vary in number. 



The same general principles apply to the fusion of homo- 

 logous parts ; and with respect to mere cohesion there is pro- 

 bably always some degree of fusion, at least near the surface. 

 When two embryos during their early development come into 

 close contact, as both include corresponding gemmules, which must 

 be in all respects almost identical in nature, it is not surprising 

 that some derived from one embryo and some from the other 

 should unite at the point of contact with a single nascent cell or 

 aggregate of cells, and thus give rise to a single part or organ. 



