3^8 ON THE NUMBER OF POLAR BODIES AND [VI. 



concerning the expulsion 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 

 conclusion 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 hterature 

 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 fertilization, and that there are very numerous 

 cases known from almost all groups of the animal kingdom in 

 which it is perfect^ 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 men- 

 tioned without any explanation as to whether they are expelled 

 from the ^gg one after the other, or whether they have merely 

 resulted from the division of a single body after its expulsion. 

 In parthenogenetic eggs two polar bodies are also formed in 

 most cases, but they arise from the subsequent division of the 

 single body which separates from the ^gg. But such subse- 

 quent division is only of secondary importance as far as the ^gg 

 itself is concerned, and is also unimportant in the interpretation 

 of the process. The essential nature of the process is to be 

 found in the fact that the nucleus of the egg-cell only divides 

 once when parthenogenesis occurs, but twice when fertilization 

 is necessary, and it is of no importance whether the expelled 

 part of the nucleus of the cell-body atrophies at once, or after 

 it has undergone division. We have, therefore, to distinguish 

 between primary and secondary polar bodies. If this distinction 

 is recognized, and if we leave out of consideration all doubtful 

 cases mentioned in literature, such a large number of well- 

 estabhshed observations remain, that the existence of two 

 primary polar bodies in sexual eggs, and neither a smaller nor 

 a larger number, may be considered as proved. 



Hence follows a conclusion which I believe to be very signi- 

 ficant,— the difference between parthenogenetic and sexual eggs 

 lies in the fact that in the former only one primary polar body 

 is expelled, while two are expelled from the latter. When, in 



