186 NUCLEOCYTOPLASMIC RELATIONS 



lar mutant in the honey bee Apis mellifera. The implications are 

 obvious. An accessory sperm nucleus cannot, in general, undergo 

 cleavage as readily as a zygote nucleus, but some genetic differ- 

 ence in Whiting's and Rothenbuhler's stocks allows both the 

 accessory sperm nucleus and zygote nucleus to enter cleavage 

 ( Fig. 7 ) . Rothenbuhler ( 1955 ) has found that the genetic factor 

 for allowing sperm nuclei to be equipotent with zygote nuclei 

 in their ability to enter cleavage has as its basis a modified form 

 of cytoplasmic inheritance. Oddly enough, the influence can be 

 built up in other stocks after several generations of matings by 

 males from the gynandromorph-producing strain (Rothenbuhler, 

 1955; Rothenbuhler and Gowen, 1955). This is indeed very in- 

 teresting and, as an ideal nucleocytoplasmic interaction, no better 

 example can be found. Normally, an influence must exist in the 

 egg cytoplasm which prevents excess sperm nuclei from dividing 

 as soon as a zygote nucleus forms; this indicates that a substance 

 diffuses with extreme rapidity from zygote nucleus to cytoplasm 

 to sperm. It appears that the mutant honey bee lacks the ability 

 to produce the diffusible agent, Fankhauser (1925) demon- 

 strated the existence of a similar condition in amphibian eggs by 

 a series of elegant experiments in which he separated l^y constric- 

 tion an accessory sperm nucleus from the activated zygote 

 nucleus. 



Several experiments have been carried out by the author in 

 which organization of the Habrobracon egg has been radically 

 disrupted by breaking the egg and forcing the egg nucleus into 

 the exudate. Of utmost interest is that mitosis under such condi- 

 tions can occur at all. A typical experiment begins when timed 

 eggs have just finished meiosis. Each egg was torn from one end 

 to the other and quickly covered with mineral oil to prevent 

 evaporation. After being incubated for 1 hour longer, the eggs 

 were fixed and stained. In most cases, the nuclei were in the 

 exudate and freely dividing when fixed. Extended experiments 

 have been performed on eggs that were broken and in which 

 cleavage was allowed to continue within the broken membranes 

 (Table I). When newly oviposited eggs were broken widely at 

 their posterior ends and covered with mineral oil to prevent 



