THE ACTIVATION OF UNFERTILIZED EGGS 107 



percentage of ova segmenting with any semblance of reg- 

 ularity decreased perceptibly with the age of the ova. In 

 the group of ova recovered at 24 to 96 hours after copulation 

 16 of the ova classified as irregular exhibited one large cell 

 and ''many polar bodies." In fact, 23 or about half of all 

 the ova called ''irregular" are of this type. A number of 

 ova, particularly in the 24 to 96 hour group exhibited "many 

 polar bodies" and a varying number of larger cells. The 

 rest of the ova classified as irregular were either "many- 

 celled" with indistinct cell outlines, or contained cells of 

 unequal size traceable, probably, to the differential division 

 of early blastomeres. 



Now this fact that the younger ova tend to segment 

 regularly is presumably related to the state of the egg cyto- 

 plasm. The older ova undoubtedly undergo a certain degree 

 of degeneration as they progress down the tubes, and the 

 degree of cytoplasmic degeneration is probably related to 

 the regularity of the subsequent development in culture. 

 The problem is unfortunately complicated by the fact that 

 all ova in culture stop segmenting and degenerate after 

 some time. In these experiments it is probable that prac- 

 tically no development occurs after the ova have been in 

 culture for 36 hours. The time in which the ova may exhibit 

 their potentialities for parthenogenetic development is, un- 

 der the conditions of these experiments, therefore extremely 

 limited. The surprising fact is that such a large proportion 

 of the ova do exhibit a degree of development that must be 

 classified as parthenogenetic. 



The morphology and cytology of parthenogenetic ova 

 have been studied in a number of invertebrate forms where 

 parthenogenetic development has been induced by various 

 methods of treatment. In almost all cases a very large 

 proportion of the parthenogenetic ova exhibit marked ir- 

 regularities in development {e.g., Wilson, 1901; Scott, 1906; 

 Morris, 1917). In fact all the irregular types described here 

 have been observed in artificially parthenogenetic inverte- 

 brate ova. The proportion of regular divisions observed 



