38o PERMANENT HYBRIDS 



prematurely at the prophase of meiosis ; they do not pair with the 

 other five and the first division is equational. At the second division 

 the precocious chromosomes pass to one pole and the others then 

 pass to the opposite pole. The two sides of the spindle are formed 

 separately, as in the haploid bee, where only one side is effective. 

 It appears that the two sets of five chromosomes are those derived 

 from opposite parents, and that they are therefore permanently 

 separated in phylogeny. The whole set is differentiated in regard 

 to sex. The behaviour in another coccid, Lecanium hemispherictim 

 and Phenacoccus (Hughes-Schrader, 1935), is similar (Thomsen, 

 1927). 



In the male Protortonia (2n = 5), on the other hand, the condition 

 is probably intermediate between that in Psendococcus, and in the 

 normal type of sex-determination in other Hemiptera. There is no 

 distinction between the two sets, and pairing takes place between 

 two chromosomes, the other three remaining unpaired. The four 

 groups lie in separate vesicles at the first division and the 

 chromosomes divide equationally. But at the second division the 

 chromosomes arrange themselves in a row or chain which lies 

 axially in the spindle and divides so that two chromosomes at one 

 end go to one pole and the other three to the other. Their order is 

 not constant, but one of the chromosomes which is definitely 

 smaller than the rest lies at one end of the chain in three-quarters 

 of the nuclei. This is probably the arrangement giving the effective 

 segregation, which in this case is of one kind only — probably that 

 giving the separation of unchanged maternal and paternal 

 chromosomes. Diagrammatically, on this hypothesis, the 

 chromosome relationship can be represented thus : $, AABBCC ; 

 eggs, ABC ; ^, AABBCC ; sperm, ABC (^-producing) ; and AB^ 

 ((^-producing). Since B and Bj have no opportunity of crossing 

 over, and B^ is transmitted exclusively by the male sex, they will 

 be permanently separated in phylogeny (as the whole complexes 

 are in Pseudococctis). It may be noted parenthetically that it does 

 not necessarily follow that they are not homologous or even identical 

 because they fail to pair, for genetic factors must undoubtedly have 

 been the original cause of this failure (as in facultative 

 parthenogenesis, q.v.). But it does follow that since they do not 



