278 Causes and Course of Organic Evolution 



tion is at once draTvn in, and partly in this way, partly by its 

 own movements, the microgamete penetrates the macrogamete, 

 and its pronucleus reaches the female pronucleus. 



"No sooner is the entry of the microgamete completed than 

 a clear membrane, gradually increasing in distinctness, appears 

 over the whole surface of the zygote, excluding the less for- 

 tunate microgametes, wliich die off and break up. The clear 

 membrane very soon becomes an exceedingly tough protective 

 envelope, the oocyst" (109: 219). 



Highly interesting for our present purpose is the following, 

 "Schaudinn has observed some curious points of consider- 

 able interest in this process. Before the macrogamete has 

 expelled the fragments of its karyosome [nucleolus mihi] from 

 the cytoplasm, it is not attractive to the microgametes, but no 

 sooner has it done so than they are drawn to it as by a magnet. 

 The attraction, which is evidently exerted by the substance 

 of the karyosome [nucleolus mihi] itself, acts very suddenly, 

 and reaches from 48/>i to 130/x. If exerted near to developing 

 microgametes, it stimulates them to great activity; even still 

 imperfect microgametes then develop flagella, and in their 

 struggles to free themselves from the microgametocyte they 

 carry away lumps of protoplasm with them. The substance 

 of the karyosome [nucleolus] seems to be absorbed by the 

 microgametes that swarm to it, and the remarkable fact was 

 observed that the attractive power of the macrogamete was 

 limited as regards the number of microgametes drawn to it, 

 the usual number being about twelve or fourteen. When 

 tliis number was made up, fresh microgametes approaching 

 the macrogamete were no longer attracted. After the sub- 

 stance of the karyosome has dissolved up, a fresh attraction 

 seems to be exerted by the female pronucleus, which travels 

 to the surface. 



"The fusion of the two pronuclei in the zygote takes j^lace 

 in a very remarkable manner. The female pronucleus passes 

 back to tlie center of the zygote and becomes drawn out in 

 the form of an elongated spindle, on which the chromatin 

 granules are arranged in parallel rows running in a meridional 



