266 FRANZ SCHRADER. 



found a serious error in his counts of somatic chromosomes, 

 which they believed in reality to be 24 and not 10 as he had 

 reported. Furthermore, reduction occurred in the ordinary way, 

 just as in Tomoptcris. Gregoire ('09) in going over the same 

 slides maintained that the Schreiners were correct in that the 

 case was one of ordinary reduction, but that they in turn had 

 made an error in the chromosome counts. The somatic number 

 is about 12, and the reduced number 6. Lastly Wassermann 

 ('n, '12, and '13) procured new material and concluded that 

 Gregoire's counts had been correct. He did not agree with 

 Gregoire as to the mode of synapsis however, and apparently was 

 unable to reach a final conclusion in this regard himself. Al- 

 though he thus does not believe that the question has received a 

 definite settlement, the fact remains that Zoogonus does not 

 represent the simple type of reduction that Weismann advanced 

 in a hypothetical way. 



If my hypothesis is correct, the male of Pscudococcus nip a; is 

 heterozygous in that it has five sex-chromatin carrying chromo- 

 somes and five chromosomes purely autosomal in character. 

 Crossing over would not occur in these chromosomes. It would 

 occur however in the female, in which the ten chromosomes are 

 composed of five homologous pairs. If the male represents i X, 

 the female with ten sex-chromatin carrying chromosomes repre- 

 sents 2 X. 



SUMMARY. 



1. The diploid number of chromosomes in Psendococcits nipce 

 is ten in both sexes. 



2. In the maturation of the egg, five tetrads are formed and 

 reduction is probably normal. 



3. In the spermatogenesis, five chromosomes are developed 

 before the others, and 'these tend to remain grouped together. 



4. No tetrads are formed, and in reduction five chromosomes 

 go to one pole (supposedly those evolved first) and five to the 

 other. 



5. Explanation of this seemingly anomalous behavior is to be 

 sought in the fact that five of the chromosomes carry sex 

 chromatin. 



