x] ARTIFICIAL PARTHENOGENESIS IN FROGS 149 



into blastomeres is more or less suppressed. In the eggs of 

 Mactra KOSTANECKI observed a process of intranuclear 

 division of the chromosomes in the first division of the 

 parthenogenetic egg, by which he supposes that the normal 

 somatic number may be restored, instead of the reduced 

 number present in the egg-nucleus after maturation. 



Finally, it has been found possible to cause the eggs of 

 Frogs to develop parthenogenetically, although the methods 

 used for Invertebrates are not effective for either Fishes or 

 Amphibia. The first successful experiment was by GUYER, 

 who injected frog's blood into the eggs. BATAILLON then 

 succeeded in producing parthenogenesis by merely pricking 

 the eggs which were smeared with blood, and LOEB and 

 BANCROFT have shown that the presence of blood is not 

 absolutely essential. BATAILLON believed that the develop- 

 ment was caused by introduced fragments of leucocytes, 

 which act as " catalysers," but an ingenious suggestion has 

 been made by HERLANT with regard to the function of the 

 blood, the introduction of which certainly facilitates develop- 

 ment. He finds that around each leucocyte or fragment a 

 small aster is produced, and the presence of these asters 

 reduces the volume of protoplasm over which the main 

 division spindle must take control before actual cell-division 

 can be initiated. HERLANT, in fact, maintains that all 

 methods of inducing artificial parthenogenesis are either 

 such as to increase the size of the division spindle, or to 

 reduce the effective volume of protoplasm which it must 

 control, and so make possible a beginning of segmentation 

 which would otherwise fail to be effective. In the experi- 

 ments of LOEB and BANCROFT, in which development was 

 induced by simple pricking without any introduction of 

 foreign cells, parthenogenesis is probably caused by an 

 alteration of the surface due to the prick, comparable with 



