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FRANZ SCHRADER. 



Menniria (McClung, '05) where the sex chromosome and the 

 autosomes are distinct, but the former is attached to one of the 

 latter. It is at present unnecessary to go into the relation of the 

 two conditions, though very possibly they represent two distinct 

 steps in the phylogeny of sex chromosomes. 



Their subsequent behavior is more or less analogous to that of 

 the X Y pair in other forms. This pair does not form a tetrad 

 in the ordinary sense simply because its members are not homo- 

 logous, or better perhaps, because neither has a true synaptic 

 mate. When as in the homozygous state both members of a pair 

 of sex chromosomes are homologous, synapsis and tetrad forma- 

 tion occur just as in the autosomes. This fact is plainly borne 

 out in the oogenesis of many Hemiptera (Morrill, '10) as well as 

 in the growth and maturation phenomena of the eggs of Pscudo- 

 coccus nipcc. It is thus to be assumed that if in the present case 

 of the spermatogenesis of Pseudococcus nipce the sex chromatin 

 were distributed equally over the ten autosomes, the pairs would 

 be homologous and tetrads would be formed in the usual way. 



The cytological evidence indicates nothing that should render an 

 equation division exceptional in nature, and it does indeed occur in 

 the usual manner. The second division witnesses reduction in 

 that the autosomes carrying sex chromatin go to one pole while 

 the purely autosomal chromosomes go to the opposite pole. 

 Taking recourse to a parallel case once more, attention may be 

 drawn to the two X chromosomes in Syroniastcs which always go 

 the same pole in reduction (Wilson, '09). Similarly, the multiple 

 X of the Reduviidae always goes to one pole, although this is not 

 an exactly parallel case since it is probably the product of frag- 

 mentation of a single X. 



Thus to repeat what has already been intimated for the present 

 case, the distribution of the chromosomes to their respective poles 

 in the reduction division may be explained on the ground that we 

 are concerned with five pairs of chromosomes. The members 

 of each pair are homologous except for the fact that one of them 

 in each instance carries a certain amount of sex chromatin. The 

 presence of the latter does not influence the behavior of the 

 chromosome pairs in reduction and the members of each pair go 



