AUGUST WEISMANN 357 



of fertilization, and also of parthenogenetic development, if it does 

 not receive a spermatozoon. It is in the power of the queen-bee to 

 produce male or female individuals : by an act of will she decides 

 whether the egg she is laying is to be fertilized or unfertilized. She 

 "knows beforehand" whether an egg will develop into a male or a 

 female animal, and deposits the latter kind in the cells of queens and 

 workers, the former in the cells of drones. It has been shown by 

 the discoveries of Leuckart and von Siebold that all the eggs are 

 capable of developing into male individuals, and that they are only 

 transformed into ''female eggs" by fertilization. This fact seems to 

 be incompatible with my theory as to the cause of parthenogenesis, 

 for if the same egg, possessing exactly the same contents, and above 

 all the same segmentation nucleus, may develop sexually or partheno- 

 genetically, it appears that the power of parthenogenetic development 

 must depend on some factor other than the quantity of germ-plasm. 

 Although this appears to be the case, I believe that my theory en- 

 counters no real difficulty. I have no doubt whatever that the same 

 egg may develop with or without fertilization. From a careful study 

 of the numerous excellent investigations upon this point which have 

 been conducted in a particularly striking manner by Bessels (in addi- 

 tion to the observers quoted above), I have come to the conclusion that 

 the fact is absolutely certain. It must be candidly admitted that the 

 same egg will develop into a drone when not fertilized, or into a 

 worker or queen when fertilized. One of Bessels' experiments is 

 sufficient to prove this assertion. He cut off the wings of a young 

 queen and thus rendered her incapable of taking "the nuptial flight." 

 He then observed that all the eggs which she laid developed into 

 male individuals. This experiment was made in order to prove 

 that drones are produced by unfertilized eggs ; but it also proves 

 that the assertion mentioned above is correct, for the eggs which 

 ripen first and are therefore first laid, would have been fertilized had 

 the queen been impregnated. The supposition that, at certain times, 

 the queen produces eggs requiring fertilization, while at other times 

 her eggs develop parthenogenetically, is quite excluded by this experi- 

 ment ; for it follows from it that the eggs must all be of precisely the 

 same kind, and that there is no difference between the eggs which re- 

 quire fertilization and those which do not. 



