IVIULTIPLTCATiON P.Y GE^i^rATION 1 69 



which multiply by gemmation, we cannot assume that this proc- 

 ess has a common origin. But although it may have arisen 

 independently in the various subdivisions of the animal king- 

 dom, the history of its origin will have been essentiallv the 

 same in all cases, for ' blastogenic ' idioplasm must have become 

 differentiated from the germ-plasm even in the egg-cell, as all 

 the determinants of the species are contained only in the latter. 

 Even at the present day the blastogenic idioplasm must be 

 present as such in the germ-plasm, for otherwise it could not 

 have undergone independent and hereditary variation : the for- 

 mation of medusie from polypes by gemmation, and manv other 

 cases of alternation of generations, prove that this has actually 

 occurred. 



Balfour attempted to derive the process of budding from a 

 division of the fertilised ovum into two separate parts, such as 

 has been observed in certain animal forms, and which leads to 

 the formation of two individuals. He imagined that if this 

 process of doubling were transferred to a later ontogenetic stage, 

 budding would result, and expressed his views as follows : — 

 ' While it is next to impossible to understand how production 

 of a bud could commence for the first time in the adult of a 

 highly organised form, it is not difficult to form a picture of the 

 steps by which the fission of the germ might eventually lead to 

 the formation of buds in the adult state.'* Unfortunately this 

 gifted observer did not work out this idea in detail : it seems to 

 me. however, that the derivation of budding from the doubling 

 of the fertilised ovum by division is not so simple or self-evident 

 as we might expect at first sight. 



Let us suppose that a fertilised ovum became capable of 

 dividing into two parts: these two first segmentation -cells 

 would not then be blastomeres, but would correspond to egg- 

 cells, each of which could give rise to an entire animal. But this 

 could not be called gemmation, nor would the latter process 

 occur if the doubling were transferred to a later stage : — this 

 would only cause a multiplication of the egg-cell, which would 

 result in the formation of four, eight, .sixteen, &c.. ova, instead 

 of two. 



If, however, we .suppose that the division of the egg is of such 

 a kind that the two halves at first remain together so as to form 



* F. M. Balfour, ' Comparative Embryology,' Vol. i., Introduction, p. 13. 



