ARTIFICIAL PAUTHENOGENESIiS AND FERTILISATION. 499 



alternate cliauges of disiutegration and recoiisti-uction with- 

 out division of the cytoplasm. Radiations appeared and dis- 

 appearedj and after three cycles^ owing to the segmentation 

 of the portions containing the sperm nucleus, the egg-nuclear 

 portion became detached and disintegrated. In another 

 experiment the egg-nuclear portion underwent changes of 

 form suggesting abortive attempts at cleavage. The mitotic 

 transformation of the egg nucleus was not synchronous with 

 that of the sperm nucleus, but always a little behind. 



These observations show that under the conditions of the 

 experiments the egg nucleus is excited to division without 

 direct contact with the sperm nucleus or aster, but that the 

 mitotic phenomena are ineffective to produce cytoplasmic 

 cleavage. Ziegler refers this to the general stimulation of 

 the egg by the spermatozoon, manifested also by the throw- 

 ing off of the vitelline membrane. Boveri lias shown that 

 the same phenomena occur in egg fragments produced by 

 shaking some minutes after fertilisation, and he (1902) refers 

 to cases of this kind in which he has observed divisions of 

 the nucleus followed by cell cleavage. The division was 

 repeated a second time, and thus the four- cell stage was 

 reached, but development then ceased. Another example of 

 the effect of this general stimulation is to be seen (Boveri, 

 1902) in the cases in which the egg is incited to throw off the 

 polar bodies by the entrance of the spermatozoon. 



This brings me to a further reference to Wilson's observa- 

 tions on etherised eggs (1901 b). As has already been said, 

 under this treatment the sperm and germ nuclei remain 

 apart and undergo independently karyokinetic transforma- 

 tion. "The most striking fact is that, while the sperm aster 

 often gives rise to a perfect and symmetrical bipolar figure, the 

 egg nucleus in a great number of cases produces a monaster, 

 which seems at first incapable of resolving itself into a 

 bipolar figure." In typical cases the egg nucleus gives rise 

 to a monaster such as described by Hertwig ('96), and such 

 as occurs in magnesium eggs. While the egg monaster does 

 not at first give rise to a dicentric figui'C, it does so later, as 



