Experiments on Echinus' eggs 91 



perhaps tends to show how important this attraction property is 

 for the normal development of embryos. The fact that under 

 these peculiar conditions the living blastomere does not show 

 attractive properties does not necessarily upset the hypothesis 

 that attraction is a general truth, any more than the fact that 

 although a glass vesicle sinks in ordinary water, yet, if a certain 

 percentage of some salt be added to the water it exhibits repulsion 

 rather than attraction to the centre of the earth, upsets the 

 universality of the force of gravitation. In the latter case a 

 better knowledge of the laws of gravitation enables one to under- 

 stand the "abnormality," whereas the abnormal behaviour of 

 segments developing in sea water without calcium salt remains 

 for the present a mystery. It has been suggested in this particular 

 case that the action of the calcium salt is to help in the formation 



N. 



of a cementing material which in its absence is not formed. This 

 however seems to me hardly a sufficient explanation, for the 

 presence of a cement would not of itself account for the flattening 

 of the segments against one another, nor for the fact that on adding 

 again the necessary calcium, adherence follows. 



The idea of Entelechy developed by Driesch in his Gifford 

 Lecture is of the most intense interest; but it must be allowed 

 that the conception is almost mystical. 



Now, although the development of the egg up to the formation 

 of the archenteron is, as compared with the later stages of ontogeny 

 or still more as compared with regenerative processes, almost in- 

 finitely simple, yet nevertheless it involves stages of the greatest 

 importance, namely establishment of the gut cavity, and differen- 

 tiation of the tissue into the groundwork of the ectodermal, and 

 endodermal tissues, that is to say, the formation of layers whose 

 subsequent fate can be foretold. 



If Entelechy is the ruling influence of life, ought it not to be 

 the ruling influence in such a process as the gastrulation of the 

 Amphioxus by invagination of a blastula? If it can be shown 

 that this process is explicable by a general application of a simple 

 force in combination with other well-known factors, the probability 

 of which is claimed to have been shown in the foregoing pages and 

 elsewhere not only in Amphioxus, but in Lepus and Rana, may we 

 not doubt whether, if it were possible to analyse the almost 



