THE ACTIVATION OF UNFERTILIZED EGGS 105 



so that one may observe in the same culture the different 

 types described. Figure 10 is a photograph of an ovum 

 segmented to about 20 cells and apparently with a marked 

 degree of regularity. When we come to consider ova seg- 

 mented into 20 and more cells the interpretation of the 

 course of their development becomes difficult because of a 

 peculiar complication. The o\aim of Figure 11 offers a per- 

 tinent illustration. It w^as recovered from the tubes at 

 37 hours after copulation and was in the 1-cell stage. 

 Six hours later it presented the appearance shown in the 

 photograph. It has apparently segmented into about 36 cells 

 in the course of 6 hours. This means astonishingly rapid 

 segmentation. As a matter of fact what probably occurred 

 was a complex fragmentation of the entire ovum. In the 

 course of filming an ovum recovered at 29 hours and 20 min- 

 utes after copulation the course of such fragmentation was 

 observed. After an initial period of quiescence the ovum 

 underwent a period of activity which resulted in the sudden 

 appearance of many small ^^ blast omeres." This was fol- 

 lowed by a complete quiescence with the cessation of all 

 cytoplasmic movements. The ''cells" of this fragmented 

 ovum, however, were not at all distinct in form or outline. 

 One may observe ''many-celled" ova. in culture that pre- 

 sented this vagueness of cell outline, but we have also seen 

 well advanced ova in which the component blastomeres were 

 as distinct and clear as in the normal fertilized ovum. Inter- 

 pretation must, therefore, proceed slowly until the exact 

 mechanics of division in vitro is thoroughly investigated. A 

 certain amount of light, however, is shed on the problem by 

 the consideration given below to the relation between the 

 age of the ova and the nature of the development observed. 

 Figures 12 and 13 are photographs of two ova recovered at 

 73 hours and 40 minutes after copulation. They were 

 photographed after having been 45 hours in the same cul- 

 ture. Note the remarkable regularity of the cells of the ovum 

 of Figure 13. The ova of Figures 14 and 15 represent types 

 ordinarily described as "with many polar bodies." Both 



