THE CHROMOSOMES OF PSEUDOCOCCUS NIP.E. 263 



As has already been stated, oogenesis very probably follows 

 ordinary lines. The ten chromosomes constituting the diploid 

 number are composed of five homologous pairs, and these synapse 

 and form tetrads. Reduction is very probably normal, and re- 

 sults in a pronucleus with five chromosomes. 



In the spermatogenesis, the spermatogonial divisions, like the 

 somatic divisions, also occur in orthodox manner. This is ap- 

 parently not true of the meiotic divisions however. In explana- 

 tion of these, the best hypothesis is one which views the various 

 developments in the light of sex chromosomal behavior and is as 

 follows : 



The central group of chromosomes which appears in the growth 

 stages of the male as the more densely staining mass contains sex 

 chromatin, equally distributed among the five chromosomes. The 

 remaining chromosomes, which stain lightly at first, represent 

 what may be regarded as purely autosomal chromatin. Granting 

 this, and the assumption does not appear unjust in the light of 

 what has been described, the seemingly peculiar development 

 becomes a natural consequence. Just as in the spermatogenesis of 

 the various Orthoptera and Hemiptera, the sex chromosomes 

 always stain more or less intensely, and as far as observable do 

 not go through the various stages of thread formation. That 

 such formation may occur earlier, or in a restricted sense even 

 while the dense mass is still irregular in outline, is not ruled out 

 by any means. The autosomal chromatin on the other hand goes 

 through all the usual steps, culminating in the formation of five 

 chromosomes. The sex chromatin contained in the five grouped 

 chromosomes will tend to explain their grouped arrangement, 

 since again as in the Hemiptera, multiple X or X and Y chromo- 

 somes show a tendency to remain in close proximity during 

 development. 



If now the sex chromosomes in Pseudo coccus nipcc are re- 

 garded homologous in every way to the autosomes, except that 

 each carries a certain amount of sex chromatin, the subsequent 

 behavior is just as would be expected. I may mention here that 

 such sex chromosomes would imply a more intimate union of sex 

 and autosomal chromatin than is illustrated bv such a case as 



