EFFECT OF HEAT ON THE EGG OF CUMINGIA. 265 



diploid and have been exposed to heat. When, however, ex- 

 amination of the preserved material is made, an unexpected 

 condition is found. As in other eggs which have been heated, 

 the chromosomes are fifty-five to sixty-five in number, but 

 instead of being like those of the diploid parthenogenetic egg in 

 size, they are not to be distinguished from those of the triploid 

 egg. The reader is referred again to text-figure I in which the 

 nuclear condition of the three kinds of eggs is shown. A is 

 the parthenogenetic egg with thirty-six chromosomes incor- 

 porated into its cleavage nucleus, B the normal one also contain- 

 ing thirty-six, and C the triploid egg with fifty-four chromo- 

 somes. The range of size of the chromosomes is about the same 

 in both kinds of fertilized eggs (B and C} notwithstanding the 

 different amounts of chromatin present in them. Plates of the 

 eggs heated after maturation are shown in Figs. 15, 16 and 17, 

 the numbers of the chromosomes being 55, 65, and 66 respec- 

 tively. 



(d) The Value of the Polar Body. The unexpected size relation 

 of the cleavage chromosomes suggests the possibility that the 

 chromatin of the polar nucleus is not, as a matter of fact, active. 

 If that were the case, the parthenogenetic egg would be actually 

 haploid, and both fertilized eggs diploid, and this would explain 

 the condition illustrated in the text-figure. It must be remem- 

 bered, however, that the polar nucleus is like the egg nucleus in 

 appearance, and that the two vesicles fuse without any evidence 

 of elimination of nuclear material. Dead chromatin is some- 

 times found in the cytoplasm of other kinds of eggs under ab- 

 normal conditions, but no such masses of chromatin are found 

 in the material preserved from these experiments. Since this is 

 so, it is difficult to believe that the polar nucleus, which was 

 formed from perfectly normal daughter chromosomes, suffers 

 complete degeneration. This is especially true when one reviews 

 the experiments (Morris, '17) by which it was shown that the 

 retention of the polar nucleus in unfertilized eggs is followed by 

 normal cleavage ; while those eggs from which it is extruded are 

 unable to develop. 



Study of the later stages of the development of heated eggs 

 confirms the belief that the polar nucleus is an active element in 



