128 ETHEL NICHOLSON BROWNE 



corresponding with the central one and the small peripheral one 

 of the first division. Female diploid groups show 24 chromo- 

 somes, including four small ones and six large ones, the third 

 pair of large ones being in all probability the X chromosomes 



(fig. 50). 



b. Comparison with the results of Pantel and Sine'y 



Pantel and Sinety, in their monograph on "Les cellules de la 

 lignee male chez le Notonecta glauca," have been concerned 

 chiefly with the growth stages and transformation into the sper- 

 matozoon, and have only incidently taken up the maturation 

 divisions. However, their criticism of the chromatic figure as 

 being "d'un type mahngre" for the study of these divisions 

 seems to me to be altogether unwarranted, for the chromosomes 

 are large, well differentiated in size, and in general seem excep- 

 tionally fine for study. Judging from the few figures that are 

 given of these stages, their material was essentially like my own 

 and was prepared in the same way, and I believe that with further 

 study would have yielded similar results. 



In the first division, they count in polar views, sometimes 12, 

 sometimes 13 chromosomes, arranged in a ring with one or two 

 in the center, but they state that they can assign no reason for 

 the discrepancy in number. However, in a part of their paper 

 dealing with abnormaUties — here the presence of small deep 

 staining corpuscles — a polar view is given, showing a group of 

 12 chromosomes surrounding one small one, the grouping and 

 size relations corresponding exactly with my figures. The large 

 chromosome, which is such a striking feature of this species, has 

 received particular attention from these authors. They call it 

 the 'chromosome exceptionelle' and describe it as a massive ir- 

 regular body giving one the impression of a double cross or a 

 system of double V's, and their figures of it in polar metaphase 

 and side anaphase are quite similar to mine. Although they are 

 convinced that it participates in both divisions, they suggest a 

 possible relationship to an accessory chromosome; they abstain 

 however from giving its exact significance. In the second divi- 



