VI.] THEIR SIGNIFICANCE IN HEREDITY. 36 1 



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 

 presented by the eggs which may develope with or without 

 fertilization. I refer to the well-known case of the eggs of bees. 

 It might be objected to my theory that the same G^gg cannot be 

 prepared for development in more than one out of the two 

 possible ways ; it might be argued that the ^gg either possesses 

 the power of entering upon two successive nuclear divisions 

 during maturation, and in this case requires fertilization ; or 

 the ^gg may be of such a nature that it can only enter upon one 

 such division and can therefore form only one polar body, and 

 in that case it is capable of parthenogenetic development. Now 

 there is no doubt, as I pointed out in my paper on the nature 

 of parthenogenesis \ that in the bee the very same egg may 

 develope parthenogenetically, which under other circumstances 

 would have been fertilized. Bessel's^ experiments, in which 

 young queens were rendered incapable of flight, and were thus 

 prevented from fertilization, have shown that all the eggs laid 

 by such females develope into drones (males) which are well 

 known to result from parthenogenetic development. On the 

 other hand, bee-keepers have long known that young queens 

 which are fertilized in a normal manner continue for a long time 

 to lay eggs which develope into females, that is to say, which 

 have been fertilized. Hence the same eggs, viz. those which 

 are lowest in the oviducts and are therefore laid first, de- 

 velope parthenogenetically in the mutilated female, but are 



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 partheno- 

 genetic 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 {Laciiudand) which expelled only one 

 polar body must have been a parthenogenetic ^^Z- But I may add that 

 we have also succeeded in directly proving the occurrence of partheno- 

 genesis in Rotifera. as will be described in detail in another paper. 



' See Essay IV, Part III. p. 229. 



^ E. Bessels, ' Die Landois'schc Theorie, widerlegt durch das Experi- 

 ment.' Zeitschr. f. wiss. Zool. Bd. XVIII. p. 124. 1S68. 



