THEIR SIGNIFICANCE IN HEREDITY. 347 



plasm itself to half of its original amount. This very point seemed 

 to me to be of great importance, because, as I had foreseen long 

 ago, and as will be shown later on, the theory of heredity forces us 

 to suppose that every fertilization must be preceded by a reduction 

 of the ancestral idioplasms present in the nucleus of the parent 

 germ-cell, to one-half of their former number. 



But before the full bearing of the phenomena could be considered, 

 it was necessary to ascertain how far they were of general occur- 

 rence. There were two ways in which this might be achieved, and 

 in which it was possible to prove that parthenogenetic eggs expel 

 only one polar body, while sexual eggs expel two. We might 

 attempt to observe the phenomena of maturation in both kinds of 

 eggs in a species which reproduces itself by the parthenogenetic 

 as well as the sexual method. This would be the simplest way in 

 which the question could be decided, if it were possible to make 

 such observations on a sufficient number of species. But the other 

 method was also open, a method which would have been the only 

 one, if we did not know of any animals with two kinds of repro- 

 duction. We might attempt to investigate the phenomena of 

 maturation in a large number of parthenogenetic eggs, if possible 

 from different groups of animals, and we might compare the results 

 with the facts which are already certain concerning the expul- 

 sion of polar bodies from the sexual eggs of so many species. 



I have followed both methods, and by means of the second 

 I have arrived already, indeed some time ago, at the certain con- 

 clusion that the above-mentioned difference is really general and 

 without exception. The first polar body only is formed in all the 

 parthenogenetic eggs which I investigated, with the valuable 

 assistance of my pupil, Mr. Ischikawa of Tokio. On the other 

 hand, an extensive examination of the literature of the subject 

 convinced me that there is not a single undoubted instance of the 

 expulsion of only one polar body from eggs which require fertiliza- 

 tion, and that there are very numerous cases known from almost all 

 groups of the animal kingdom in which it is perfectly certain that 

 two polar bodies are formed, one after the other. A number of the 

 older observations cannot be relied upon, for the presence of two 

 polar bodies is mentioned without any explanation as to whether 

 they are expelled from the egg one after the other, or whether 

 they have merely resulted from the division of a single body after 



