MULTIPLICATIOX V.Y GEMMATION 167 



arranged into main groups, one of which is supplied as accessorv 

 idioplasm to one cell of the ectoderm, and the other to one or 

 more cells of the mesoderm. The siiigle ectoderm cell gives 

 rise to the entire endoderm, but it must nevertheless not be 

 considered equivalent to those cells of the embryo which give 

 rise to the endoderm by invagination, for it forms parts which 

 are either not developed at all in the embryo, or else arise from 

 other ectoderm cells. Without entering into details here, the 

 facts may be expressed in terms of the idioplasm by supposing 

 that the ectoderm-cell from which the bud arises is provided 

 with an idioplasm which contains the whole of the determinants 

 for the endoderm, as well as a number of others, and that this 

 combination of determinants does not occur in embryogeny. 

 The mesoderm-cells of the parent which gives rise to the endo- 

 thelia, muscles, &c., of the bud, must also contain a peculiar 

 combination of determinants which is not exactlv similar to 

 that which occurs in embryogeny. The gemmation must there- 

 fore be prepared for in embryogeny by certain series of cells in 

 the ectoderm and mesoderm being provided with these groups 

 of determinants in the form of accessory idioplasm. 



A third stage is represented by the gemmation of fixed Asci- 

 dians and Salps. In these the bud originates — in the fully- 

 formed animals, or in those which are still undergoing develop- 

 ment — from three kinds of cells, viz., those of the ectoderm, 

 mesoderm, and endoderm. And here again those groups of 

 determinants which must be supposed to exist in the three 

 kinds of cells do not correspond exactly to those which must be 

 contained in the prmiary ectoderm, endoderm, and mesoderm 

 cells. In fact, no group of cells which occurs in embryogeny 

 can contain precisely the same group of determinants as does 

 the endoderm cell of the bud. A collection of determinants 

 especially adapted for budding must therefore be provided on a 

 large scale during embryogeny in this case, so that eventually 

 certain cells may receive their supply from it in the form of 

 accessory idioplasm. 



This last kind of budding resembles reijeneration verv closelv 

 as regards the idioplasm concerned in the process. It must 

 not, however, be therefore implied that the former process 

 has been derived phylogenetically from the latter. The re- 

 semblance only consists in the formation of a new ' Derson,' 

 which in both cases originates in several cells provided with 



