306 THE EVOLUTION THEORY 



norinnllv unfertilized. Only in tlie last decade of the past century 

 did the bee-keepers be<;-in to cast doubt on this so-called ' Dzierzon 

 theory'- ' ; various violent and obstinate attacks were made upon 

 it, and these were supported by new and apparently convincing ex- 

 periments- Dickel, a teacher in Darmstadt, has been particularly 

 strenuous in attempting to overthrow the old theory, by emphasizing 

 the fact that von Siebold's old investigations on bee eggs afforded 

 no convincing proof. Von Siebold made his investigations on eggs 

 freshly taken from the hive, and was never able to find spermatozoa 

 in * drone eggs ' (that is, eggs laid in drone cells and therefore 

 destined to develop into drones), while he was often able to demon- 

 strate the presence of from one to four spermatozoa in ' worker eggs.' 

 But he only examined ' drone eggs ' which were already twelve hours 

 old, and in these, as we now know, he would not have found 

 spermatozoa in any case, even if they had been fertilized, because 

 in ova at that stage the development of the embryo has already 

 fully begun, and nothing remains of the spermatozoa. In the bee, 

 according to Buttel-Reepen, the fertilizing spermatozoon is trans- 

 formed in twenty minutes after it has penetrated into the egg into 

 a minute 'sperm-nucleus' which is almost invisible even in sections, 

 and certainly nothing whatever could be seen of it by the old method 

 of squeezing the fresh ovum. 



It had therefore to be admitted that Dzierzon's theory rested 

 on an insecure foundation, and I accordingly set two of my students 

 at that time, Dr. Paulcke and Dr. Petrunkewitsch, to examine the 

 eggs of the bee anew with regard to the point in question, using the 

 greatly improved methods at their disposal. These investigations 

 have been carried out in the Freiburg Zoological Institute during the 

 last three years, and have resulted in establishing the absolute correct- 

 ness of Dzierzon's theory : the ' drone eggs ' do remain unfertilized, 

 while the eggs from which females are to develop are fertilized 

 without exception. 



In this case, therefore, we have, in the same animal; eggs which 

 can be fertilized and eggs which, without fertilization, develop 

 parthenogenetically, and it is therefore of the greatest possible interest 

 to know the state of matters in them in regard to the directive 

 divisions and the reduction of the chromosomes. 



Dr. Petrunkewitsch's investigations have shown that in both 

 cases, that is, whether a spermatozoon penetrates into the ovum or 

 does not, a twice- repeated division of the nuclear material in the 

 ovum takes place. Moreover, the two daughter-nuclei which result 

 from the second division do not, as Brauer showed was sometimes the 



