THE CELL AND ITS CONSTITUENT STRUCTURES. 145 



mature ovum. Indeed, so generally is this opinion shared, 

 that Boveri, one of the staunchest upholders of the im- 

 portance of the centrosome, regards its importation by the 

 spermatozoid during fertilisation as one of the necessary 

 conditions of segmentation. But it is difficult to reconcile 

 this assumption with the results of an investigation carried 

 on by R. Hertvvig^ on Echinoderm eggs. 



This writer, in the first place, agrees with all the recent 

 observers who have investigated these objects ; that Fol 

 was quite in error in attributing a centrosome to the Qgg. 

 In fact, the whole history of the supposed fusion of centro- 

 somes arising from the male and female cell respectively is 

 one of the best object lessons I know of wherewith to en- 

 force the remarks about methods which I prefaced to what 

 I have to say to-day. But R. Hertwig discovered that, 

 although the female cell contained no centrosome (that is, no 

 " organ of division "), this circumstance did not prevent the 

 nuclei of these unfertilised eggs, when they had been kept 

 for a sufficiently long time, from starting through the first 

 phases of karyokinesis ; and he incidentally made the in- 

 teresting discovery that certain stimulants hurried up the 

 process, so that, although normally it only begins after the 

 eggs have been extruded about two days, under the in- 

 fluence of very dilute solution of strychnine it commences in 

 about one and a half hours after extrusion. It is true that 

 for the most part the division of the nucleus was not 

 completed, but that does not affect our present argument ; 

 the important point is that in the admitted absence of 

 the so-called division oi'gan the division itself could be 

 initiated. 



But Hertwig went further with his experiments. He 

 found that by applying chloral to the spermatozoids and ova, 

 before mixing them together, he was able to inhibit the. ftisio7t 

 of the male and female nuclei, although the spermatozoid 

 still retained the power of penetrating the egg sufficiently 

 to become embedded within its protoplasm. When this 

 occurred, spindles were formed, both in connection with the 



^ " Ueb. die Entwick, des unbefruchteten Secigeleies," Fesfschr. f. 

 Gegenbaur, Bd. i., Lei[)zig, 1896. 



