EFFECT OF HEAT ON THE EGG OF CUMINGIA. 269 



of nuclear material that is present in them. If this were not so, 

 the chromosomes of the fertilized egg heated after maturation 

 would be like those of the parthenogenetic egg, instead of like 

 those of the triploid one. Various other facts indicate that the 

 appearance of these equatorial plates is not a reliable measure 

 of the amount of chromatin present. Compare, for instance, 

 Figs. 15 and 17. There are ten more chromosomes in the 

 second plate than in the first, but the increase in number has 

 evidently not been accomplished by the subdivision of some 

 members of the first group for the average size of the bodies is 

 greater in the plate which contains the larger number. Compare 

 Fig. 17 with Fig. 10 also. Fertilization and maturation were 

 normal in both these eggs, so that they undoubtedly contained 

 the same amount of chromatin, but it seems as if there were 

 more in the figure from the egg which has been heated. There 

 is, in fact, no increase in amount, for in later stages the chromatin 

 returns to the normal condition (Figs. 19 and 20). 



Apparently, in heated eggs, we have an abnormal condition of 

 aggregation of the chromatin, varying somewhat in individual 

 cases. The variations observed in the number and size of the 

 chromosomes are due to differing degrees of susceptibility to heat 

 on the part of the eggs. When the susceptibility is slight, 

 there is an increase in the number of bodies formed from the 

 chromatin; when it is greater, there is an apparent increase in 

 the amount of this material. It may be noted that the slighter 

 abnormality is found in eggs heated before fertilization. At this 

 period few eggs are destroyed by the heat, even if the exposure 

 is prolonged to ninety minutes. After fertilization and matura- 

 tion have taken place, it is difficult to warm the eggs for even 

 thirty minutes without killing a large number; and it is in the 

 chromosomes of these eggs that the greatest degree of abnormality 



is observed. 



DISCUSSION. 



In 1910, Jordan studied the normal cytology of Cumingia, 

 and concluded that in this animal the chromosomes are not 

 persistent and individual cell organs. He based his conclusion 

 on two facts; first, that they cannot be followed through the 

 resting stage of the cell cycle; and second, that they undergo 



