486 THOMAS Ho BRYOK. 



knowD; which tend to the production of artificial partheno- 

 genesisj but that in the case of the Annelids there is evidence 

 to show that certain Ions may have a specific effect. 



According to Loeb (1902) the solutions must act, first, by 

 favouring the solution or dissolution of the nuclear mem- 

 brane; and second, by changing, in some sense, the physical 

 properties of the protoplasm (viscidity, etc.). 



Mathews (1900), as a conclusion from his experiments on 

 Arbacia eggs, pointed out that the known methods of causing 

 liquefaction in protoplasm will induce karyokinesis in these 

 eggs, and also shows that loss of water has a liquefying 

 action. 



Before considering further the bearing of the physiological 

 and physico-chemical conceptions regarding fertilisation, I 

 shall proceed to the morphological changes which have been 

 described in unfertilised eggs which undergo parthenogenetic 

 development. 



R, Hertwig (1896) studied the changes in the egg after 

 treatment with strj^chnine. On the breaking down of the 

 nucleus, half spindles, and in a few cases whole spindles, 

 supposed to arise from the fan spindles, were foimied. The 

 fan spindle fibres he regarded as derived from the achro- 

 matic network of the nucleus. The chromosomes derived 

 from the nucleoli became attached to the primary rays. 

 Later, protoplasmic rays also appeared, centering on the 

 focal point of the half spindle. At this central point, and 

 derived from the central parts of the rays, there appeared a 

 rounded body resembling in every way a centrosome, though 

 none such was to be found before the nucleus broke down. 

 The body was an ovocentrum, formed from the achromatic 

 poi-tion of the nucleus, and, according to Ilertwig-, the 

 'individualised centrosome is ultimately a derivative of the 

 nucleus — is, in fact, an achromatic nucleus. 



Doflein (1897), contrariwise, examined the phenomena 

 of karyokinesis of the sperm nucleus in eggs which, after 

 fertilisation, had been treated by chloi*al solution after the 

 manner of the experiment of 0. and 11. Ilertwig. The nuclei 



