S pcrtnatogcnesis 477 



both divisions, while the odd chromosome, which divides only in 

 the first division, is the chromatin nucleolus of the rest stage and 

 one of the large chromosomes of the spermatogonia. He main- 

 tains that Paulmier made a mistake also in the spermatogonial 

 number, which is always odd. Foot and Strobell ('07), by the use 

 of smear preparations and photo-micrographs, have attempted to 

 show that Wilson is in error in his observations on the spermato- 

 genesis of Anasa. They find that the odd chromosome acts essen- 

 tially like any other chromosome, is made up of two spermatogonial 

 chromosomes and divides in both spermatocyte divisions, its only 

 peculiarities being that it does not appear as a tetrad in prophase 

 and occasionally divides later than the other chromosomes in 

 metaphase. They attempt to show that the chromatin nucleolus 

 of the rest stage is not a chromosome, but dissolves before meta- 

 phase like a plasmosome. Wilson ('07) has carefully gone over 

 his preparations and still thinks that his former conclusions are 

 correct. There is need of more work with smear preparations to 

 test their reliability. 



Gross ('04), in his work on Syromastes, apparently confuses the 

 m-chromosomes with the odd chromosome much as Paulmier did. 

 In Pyrrhocoris apterus ('06) he finds the odd chromosome bival- 

 ent but dividing in only one spermatocyte division. 



Montgomery ('01 a) calls the odd chromosomes of the Hemip- 

 tera "chromatin nucleoli" and considers that they may vary in 

 number and valence. He explains them as chromosomes on the 

 way to disappearance during progressive evolution. His results 

 show many discrepancies which have since been explained by 

 Wilson ('05b and '05c). 



Wilson groups the Heteroptera into three classes, those with an 

 unequal pair of heterochromosomes, those with an odd chromo- 

 some and m-chromosomes, those with an equal pair of hetero- 

 chromosomes. In the first class, the chromosome number in the 

 second spermatocyte is one less than in the first spermatocyte. 

 This is due to the fact that the conjugation of the unequal pair does 

 not take place until after the first spermatocyte division. This is 

 the most direct evidence yet found for Montgomery's synapsis 

 hypothesis, for the small chromosome can be proved to be paternal, 



