188 INTERNAL FACTORS IV. i 



in two or more blastomeres, and in the following an excessive 

 number of small cells was formed (Fig. 95). In a less dilute mix- 

 ture (16% fresh water) the blastulae divided to form each two 

 Plutei. Again by shaking the eggs in the eight-celled stage the 

 blastomeres were disarranged and made to lie almost in one plane ; 

 micromeres were, however, formed as usual from the vegetative 

 cells, but not, of course, in the normal position (Fig. 96). In 

 spite of these very considerable alterations in the size and posi- 

 tions of their constituent cells all these ova nevertheless gave rise 

 to perfectly normal larvae. 



By the use of calcium-free sea-water either the mesomeres or 

 the macromeres and micromeres were separated into two groups. 

 In the latter case the larva had two guts, in the former a normal 

 larva resulted, so that, as Driesch points out, the ectoderm at the 



FIG. 96. Disarrangement of the blastomeres of Echinus by shaking, 

 a, eight cells ; b, sixteen cells ; notice that the micromeres are not close 

 together. (After Driesch, 1896.) 



antiblastoporic (animal) pole must in this case have been formed 

 from the macromeres. 



The conclusion to be drawn from these experiments seems 

 obvious ; not only the nuclei, but the parts of the cytoplasm 

 too are equivalent; within at any rate fairly wide limits their 

 normal arrangement may be disturbed without affecting in the 

 least the normality of subsequent development ; or, as Driesch 

 phrased it, the destiny of a nucleus or blastomere is not deter- 

 mined by its original situation in the preformed structure of the 

 egg, rather it is a function of its position in the whole embryo 

 to which that egg gives rise. Its character is decided not by 

 ifs origin, but by its final position. 



Whether there really is a limit to the rearrangement is a 

 question which must be reserved for future discussion. We are 



