264 MARGARET MORRIS HOSKINS. 



more chromosomes are present here than in the normal egg, but 

 the exact numerical relations cannot be determined. The most 

 interesting comparison to be made is with the parthenogenetic 

 egg. Here, as has been said, the chromosomes are so distinct 

 that they can be counted, and the number is about the same as 

 that found in fertilized eggs in which the polar bodies have been 

 suppressed. Figs. 13 and 14 are from the first cleavage of 

 parthenogenetic eggs, in which the numbers of the chromosomes 

 are 46 and 47 respectively. In other cases as many as sixty-one 

 chromosomes have been found (Morris, '17). The general shape 

 of the bodies is similar in parthenogenetic and in heated fertilized 

 eggs; spherical bodies and short thick rods are found instead of 

 the normal threads. A striking difference is seen, however, in 

 the size of the individual chromosomes, which is considerably 

 greater in the fertilized than in the parthenogenetic egg. This is 

 most clearly respresented in text-figure I, in which the chromo- 

 somes are arranged in rows, graded according to size. A repre- 

 sents the chromosomes of the parthenogenetic egg, C those of 

 the fertilized egg in which maturation has been suppressed. The 

 smallest members of the two groups are about equal in size, but 

 almost half of those in the fertilized egg are larger than the largest 

 from the parthenogenetic one. A natural explanation of this 

 difference in size is suggested by the fact that while the suppres- 

 sion of the polar body gives the parthenogenetic egg a diploid 

 amount of chromatin, the same process makes the fertilized egg 

 triploid. As the number of chromosomes is the same in the two 

 cases, we might expect their size to be greater in the egg that 

 contains the larger amount of chromatin. This was, in fact, 

 the explanation given in a preliminary report (Morris, '17), but 

 further experiments have shown that it is not entirely correct. 

 A control series of experiments was made in which eggs were 

 subjected to heat after the formation of the polar bodies had been 

 completed. In these, the effects of heat are shown, separated 

 from any effect of the retention of the polar nucleus. The 

 comparison of the parthenogenetic eggs with those that have 

 been fertilized and heated before maturation leads one to expect 

 that eggs heated after maturation will show cleavage* chromo- 

 somes exactly like those of parthenogenetic egg, since both are 



