lyO THE GERM-PL.\SM 



only one embryo, the condition observed in a certain earth- 

 worm i^Lunibricus trapezoides^ by Kleinenberg would result. In 

 this animal the development is apparently single up to the gas- 

 trula stage, at which the separation of the two embryos first 

 occurs. Did this separation take place at a much later stage, 

 perhaps not until the two individuals are fully developed, the 

 process would not be one of budding, but only of a doubling of 

 the embrvo. 



An essential modification of this process is indispensable if 

 gemmation is to result from it, and this consists in the postpone- 

 ment of the developinent of one half of the egg. Let us suppose 

 that one of the two equivalent blastomeres of an ovum did not at 

 once undergo development at the same time as the other, but 

 remained in a unicellular condition enclosed within the embryo 

 formed from the active blastomere. and subsequently began to 

 develop when the latter had already given rise to a full-grown 

 animal: this would be a true process of gemmation. I do not 

 wish to assert definitely that the phylogeny of budding might 

 not have taken place on similar lines. A postponement and 

 subsequent transference to a later stage of ontogeny of the de- 

 velopment of one of the blastomeres is not actually inconceiv- 

 able. But such a transference must have undergone a still 

 further modification, before even the simplest form of budding 

 with which we are acquainted could arise. The shifting must 

 have occurred in a backward as well as in a forward direction ; 

 that is to sa}-, tJie division of the egg into two separate ones must 

 have been suppressed, and represented by the mere division of the 

 gerjn-plasm. 



Thus in Hydroids and other animals which multiply by bud- 

 dinof, we see, in fact, that one of the two blastomeres into which 

 the egg-cell divides does not serve, so to speak, as a reserve cell 

 for subsequent gemmation ; both blastomeres, on the contrary, 

 continue to divide, and together give rise to the embryo : and even 

 in the latter none of the cells can be distinguished as 'blastogenic- 

 cells': the cells which take part in the formation of the buds 

 only appear at a much later stage, when the polype is fully 

 formed. If therefore gemmation has in this case originated 

 from the doubling of the egg, the latter process must itself have 

 become degenerated, only the essential part of it remaining: the 

 germ-plasm concerned in it must have remained associated with 

 that of the egg-cell in the form of ' unalterable ' germ-plasm, and 



