THEIR SIGNIFICANCE IN HEREDITY. 351 



and in this case requires fertilization ; or the egg 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 1 , that in the bee 

 the very same egg may develope parthenogenetically, which under 

 other circumstances would have been fertilized. Bessel's 2 experi- 

 ments, 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, develope parthenogeneti- 

 cally in the mutilated female, but are fertilized in the normal 

 female. The question therefore arises as to the way in which the 

 eggs become capable of adapting themselves to the expulsion of 

 two polar bodies when they are to be fertilized, and of one only 

 when fertilization does not take place. 



But perhaps the solution of this problem is not so difficult as it 

 appears to be. If we may assume that in eggs which are capable 

 of two kinds of development the second polar body is not expelled 

 until the entrance of a spermatozoon has taken place, the explanation 

 of the possibility of parthenogenetic development when fertilization 

 does not occur would be forthcoming. Now we know, from the in- 

 vestigations of O. Hertwig and Fol, that in the eggs of Echinus 

 the two polar bodies are even formed in the ovary, and are therefore 

 quite independent of fertilization, but in this and other similar cases 

 a parthenogenetic development of the egg never takes place. There 

 are, however, observations upon other animals which point to the fact 

 that the first only and not the second polar body may be formed before 

 the spermatozoon penetrates into the egg. It can be easily under- 

 stood why it is that entirely conclusive observations are wanting, 

 for hitherto there has been no reason for any accurate distinction 



1 See Essay IV, Part III. p. 225. 



2 E. Bessels, ' Die Landoia'sche Theorie, widerlegt durch das Experiment.' 

 Zeitschr. f. wiss. Zool. "Bd. XVIII. p. 124. 1868. 



