ARTIFICFAL PARTHENOG l']NESIS AND FERTILISATION. 487 



did not unite, but underwent independent transformation. 

 Dofleiu, like R. Hertwig, considered the middle piece of the 

 spermatozoon as equivalent to the centrosome, and from the 

 experiments concluded^ that from the centrosorae a complete 

 spindle could form, and out of this, again, the achromatic 

 nuclear network. Thus, compared with Hertwig's results, the 

 ripe sperm nucleus contains all the parts, even as the ripe 

 egg nucleus, which are necessary for a further development. 



In Hertwig's results we have evidence of a centrosorae 

 arising from the nucleus de novo. Morgan, in 189G, 

 described the formation of artificial astrosphercs in the 

 cytoplasm of the eggs of Arbacia treated by salt solutions, 

 and from his further observations published in 1899 and 

 1900 he decided, that in spite of certain differences these 

 artificial astrospheres corresponded to the normal spheres 

 which occur at the apices of the spindles in the segmentation 

 stages; further (1900), that both artificial and normal spheres 

 are due to accumulation of a specific substance, and that theyolk 

 spheres are excluded from the substance of the astrospheres. 



His view of the astral radiations is that they serve to 

 transport the chromosomes, but are not concerned in the 

 division of the cytoplasm. 



Evidence of free formation of the centrosomes is found 

 also in the appearance of asters in the cytoplasm in various 

 forms. Echinus among them, on the breaking down of the 

 germinal vesicle in maturation. 



Boveri (1901) in essence accepted Hertwig's definition of 

 the structure described by him as an ovocentrum, and its 

 origin apparently de novo. He argued that phylogenetically 

 the centrosome is an individualised cytocentrum, derived 

 from a centro-nucleus in which the centrosome or its 

 equivalent is not differentiated from the chromatin nucleus. 

 To the nucleus of the sea-urchin egg must necessarily 

 be attributed the properties of a centro-nucleus, with the 

 capacity of producing out of itself, under the action of 

 certain stimuli, individualised centrosomes, when such fail to 

 be supplied in the normal way in fertilisation. If even under 



