350 ON THE NUMBER OF POLAR BODIES AND 



Blochmann's proof of its existence seems to me to be of especial 

 value, because the eggs of Aphidae are in many respects so unusually 

 reduced ; for instance, the primary yolk is absent and the egg- 

 membrane is completely deficient, so that we might have expected 

 that if polar bodies are ever absent, they would be wanting in these 

 animals that is, if they were of no importance, or at any rate of 

 only secondary importance. 



Hence the presence of polar bodies in Aphidae is a fresh con- 

 firmation of their great physiological importance. As bearing 

 upon the main question dealt with in this essay, Blochmann's 

 observations have an especial interest, because only one polar body 

 was found in the parthenogenetic eggs of Aphis, while the sexual 

 eggs normally produce two. The author rightly states that this 

 result is in striking accordance with my results obtained from the 

 summer-eggs of different Daphnidae, and he adds the remark, ' It 

 would be of great interest to know whether these facts are due to 

 the operation of some general law.' To this remark I can now 

 reply that there is indeed such a law : not only in the parthenogenetic 

 eggs of Daphnidae, but also, as I have since found, in those of 

 the Ostracoda and Rotifera 1 , only one primary polar body is 

 formed, while two are formed in all eggs destined for fertilization. 



Before proceeding to the conclusions which follow from this 

 fact, I will at once remove a difficulty which is apparently pre- 

 sented by the eggs which may develope with or without fertiliza- 

 tion. I refer to the well-known case of the eggs of bees. It might 

 be objected to my theory that the same egg cannot be prepared 

 for development in more than one out of the two possible ways ; 

 it might be argued that the egg either possesses the power of 

 entering upon two successive nuclear divisions during maturation, 



1 In the summer-eggs of Rotifera I have, together with Mr. Ischikawa, observed 

 one polar body, and we were able to establish for certain that a second is not formed. 

 The nuclear spindle had already been observed by Tessin, and Billet had noticed 

 polar bodies in Philodina, but without attaching any importance to their number. 

 These latter observations were not conclusive proofs of the formation of polar bodies 

 in parthenogenetic eggs, so long as it was not known whether the summer-eggs of 

 Rotifera may develope parthenogenetically, or whether they can only develope in 

 this way. Knowing now that parthenogenetic eggs expel only one polar body, we 

 may perhaps be permitted to draw the conclusion that the summer-egg of a Rotifer 

 (Lacinularia) which expelled only one polar body must have been a parthenogenetic 

 egg. But I may add that we have also succeeded in directly proving the occurrence 

 of parthenogenesis in Rotifera, as will be described in detail in another paper. 



