18 MARGARET MORRIS 



V. CYTOLOGICAL STUDY OF EGGS WITHOUT POLAR BODIES 



a. Fusion of first polar nucleus with egg nucleus. When the 

 eggs are subjected to heat, the first polar spindle moves from 

 its central position towards the periphery of the egg, as it does 

 when the egg is fertilized. In experiments in which the 

 eggs were heated to 34-35°C. the spindle is often found to be 

 contracted, as is shown in figure 49. It may be so much short- 

 ened that the chromosomes are in a compact mass in which the 

 form of individuals cannot be distinguished. In other cases, 

 however, especially in the experiments in which a lower tem- 

 perature was used, the spindle is entirely normal in this stage. 



The form of the chromosomes of the first polar spindle in 

 eggs which are undergoing parthenogenetic development is nor- 

 mal. Figure 50 illustrates an equatorial plate from a parthe- 

 nogenetic egg, and though the rings and the loop which were 

 found in some normal plates (figs. 2a and 2b) are not repre- 

 sented here, the general size and form of the chromosomes are 

 alike in the two plates. The rings are to be seen, moreover, 

 in the spindle represented in figure 49, and it is possible that 

 their absence from the plate of figure 50 is due simply to in- 

 sufficient extraction of the stain. 



In the stages following the metaphase the behavior of the 

 chromosomes is entirely normal, but a complete nuclear divi- 

 sion takes place without any corresponding cytoplasmic divi- 

 sion. Figure 51 shows clearly the beginning of the division of 

 the chromosomes. Some have already separated and are 

 grouped at the poles of the spindle; a few are just splitting. 

 The same reduction in the size of the chromosomes that occurs 

 in the fertilized eggs at the beginning of the anaphase of this 

 first maturation division, is to be seen here. In the next figure 

 (52) a shghtly later stage is represented in which all the chromo- 

 somes have divided, and in figure 53 the migration to the poles 

 of the spindle is almost finished. The splitting of the chromo- 

 somes is complete, as is shown in figures 52 and 53. If an}^ lag 

 in the center of the spindle, they are daughter-chromosomes. 

 Figure 53 represents a stage of the parthenogenetic egg corre- 



