Chap. XXVII. OF PANGENESIS. 381 



their early development was shown in the last chapter, 

 when discussing the tendency to fusion in homologous parts. 

 This affinity displays itself in the normal fusion of organs 

 which, are separate at an early embryonic age, and still more 

 plainly in those marvellous cases of double monsters in which 

 each bone, muscle, vessel, and nerve in the one embryo, blends 

 with the corresponding part in the other. The affinity between 

 homologous organs may come into action with single parts, 

 or with the entire individual, as in the case of flowers or fruits 

 which are symmetrically blended together with all their parts 

 doubled, but without any other trace of fusion. 



It has also been assumed that the development of each gem- 

 mule depends on its union with another cell or unit which has 

 just commenced its development, and which, from preceding it in 

 order of growth, is of a somewhat different nature. Nor is it a 

 very improbable assumption that the development of a gemmule 

 is determined by its union with a cell slightly different in nature,, 

 for abundant evidence was given in the seventeenth chapter, 

 showing that a slight degree of differentiation in the male and 

 female sexual elements favours in a marked manner their union 

 and subsequent development. But what determines the develop- 

 ment of the gemmules of the first-formed or primordial cell 

 in the unimpregnated ovule, is beyond conjecture. 



It must also be admitted that analogy fails to guide us 

 towards any determination on several other points: for instance, 

 whether cells, derived from the same parent cell, may, in the' 

 regular course of growth, become developed into different struc- 

 tures, from absorbing peculiar kinds of nutriment, independently 

 of their union with distinct gemmules. We shall appreciate this 

 difficulty if we call to mind, what complex yet symmetrical 

 growths the cells of plants yield when they are inoculated by 

 the poison of a gall-insect. With animals various polypoid 

 excrescences and tumours are now generally admitted 37 to be 

 the direct product, through proliferation, of normal cells which 

 have become abnormal. In the regular growth and repair of 

 bones, the tissues undergo, as Virchow remarks, 38 a whole series 

 of permutations and substitutions. « The cartilage cells may be 



J vixchow, < Cellular Pathology/ trans, by Dr. CWe, I860, pp. 60, 162, 245, 

 ' * Idem, pp. 412-426. 



