THE PROCESS OF FERTILIZATION 



SOI 



as I was able to demonstrate with the small number of ova at my 

 disposal ; but according to the investigations of Brauer on more 

 alnnidant material it appears that, while the second polar division is 

 suppressed in the majority of the ova, and the external extrusion of 

 a second polar body never occurs, the second polar division does 

 nevertheless sometimes take place. The two daughter-nuclei arising 

 from this division unite again immediately afterwards to form a 

 single nucleus, and this now functions as a segmentation nucleus. Of 

 course it again contains the full number of chromosomes, namely, 

 twice 84=168. 



In Artemia, therefore, the adaptation of the ova to partheno- 

 genetic development is not yet fully established, and the complete 

 abandonment of the second polar division seems to be phyletically 



Fig. 78. Diagram of the maturation of a parthenogenetic ovum. The number of 

 chromosomes normal to the species ]ias been assumed to be four. Uei, a primitive 

 germ-cell. MEis, a mother-egg-cell, with twice the normal number of chi-omosomes. 

 Eiz, mature ovum after the separation of the first and only polar body. RkK 



striven for, since, althougli the division still takes place, its effect is 

 neutralized innnediately afterwards. 



Among bees the state of affairs is again exceptional Here the 

 female, the so-called queen bee, possesses a capacious sperm-sac, in 

 which the spermatozoa received in copulation remain living for years, 

 and the fertilization of an ovum is effected in the usual way from 

 this sac while the egg from the ovary is passing down the oviduct. 

 The queen bee has the power of releasing some spermatozoa from the 

 receptacle, or of not doing so, and thus of fertilizing the egg, or of 

 not fertilizing it. Since the notable observations of Dzierzon and the 

 investigations of von Siebold and Leuckart which followed them, it 

 has been assumed that only those eggs were fertilized which were 

 laid in the cells destined for rearing females (workers or queens), 

 while those which were to give rise to ' drones ' or males remained 

 I. u 



