Artificial Parthenogenesis in Thalassema Mellita II3 



conditions were present, the segmenting eggs could not be dis- 

 tinguished from controls fertilized with sperm, except for the lack 

 of uniformity in the rate of division exhibited by the former, 

 especially during later stages. The rhythm of division is generally 

 more or less disturbed in eggs developing parthenogenetically, 

 and the intervals between successive cleavages are, therefore, less 

 constant than in eggs normally fertilized. All gradations, how- 

 ever, are encountered fromcases in which the rate of segmentation 

 closely approximates the normal to those exhibiting nearly every 

 stage of cleavage in the same dish at a given time. 



As in the case of the normal egg, the first furrow begins at the 

 upper pole and cuts in somewhat more rapidly here than at the 

 lower, resulting in the formation of two equal blastomeres (Fig. 5). 

 The second cleavage is also equal and gives rise to four blastomeres 

 of exactly the same size. By comparing Fig. 6 with Torrey's 

 Fig. iB ('03, p. 173), it will be seen that the same relations exist 

 here in regard to the polar furrows as are present in the normal 

 egg. The two upper blastomeres do not quite touch, and one of 

 the polar bodies has passed into the space thus left between them. 

 The four cells, constituting the first quartet of micromeres, are 

 formed at the time and nearly equal the macromeres in size 

 (Fig. 7). The cleavage space from now on increases rapidly in 

 size and frequently one or two polar bodies may be seen lying in 

 it (Fig. 40, pb). The origin of the second quartet of micromeres 

 by division of the macromeres, and the unequal division of the 

 first quartet to form the primary trochoblasts, whereby the 16- 

 cell stage is established, as Torrey has described, may be clearly 

 followed in the parthenogenetic eggs and found to be perfectly 

 normal in a great many cases. But beyond this stage I was un- 

 able to observe the cleavages with any degree of certainty in the 

 living egg on account of its opacity and the flattening down of the 

 blastomeres during the resting period, a difficulty which Torrey 

 also encountered. A i6-cell stage, drawn from the living egg, is 

 seen in Fig. 8. 



