94 KANSAS UNIVEESITY QUARTERLY. 



are in Pyrrhocoris, Undoubtedly the elements of the iirst spermc- 

 tocytes of Pyvrhocoris, like those of other insects, are quadripartite 

 — for the early stages of their formation clearly indicate this. We 

 have here another example of the fact that it is to the formative stages 

 of the chromosomes that we must look for indications of their struc- 

 ture, rather than to the mature elements themselves. 



The material derived from Pyn'hocoris is well adapted for the solu- 

 tion of many cytological problems, but I maintain that the structure 

 and divisions of the chromosomes are not one of these. Surely ma- 

 terial which requires such reasoning as Henking employed in the 

 following quotation is not of the most desirable character. He says : 

 "Dennoch bin ich der Meinung, dass die hier vorliegende Theilung 

 theoretisch einer Langstheilung gleichzusetzen sei ; denn wo ge- 

 streckte Chromosomen vorhanden sind, pfiegen sie den Polen nicht 

 ihre Enden, sondern ihre Seiten zuzukehren und also der Liinge 

 nach getheilt zu werden. Warum soUten wir hier etwas Anderes 

 annehmen "r"' 



In the germ cells of animals and plants there are wide variations 

 in size, form and manner of division of the chromosomes, but I be- 

 lieve the underlying structural principle will be found the same in all» 

 when the details are thoroughly worked out. Thus, for instance, the 

 chromosomes of Pyrrochoris and Ilippiscus differ remarkably in al- 

 most all points, if the elements in the metaphase of the first sperma- 

 tocyte are considered. If, however, we look back to the prophases, the 

 quadrii3artite nature of each is apparent. 



Too much importance cannot he laid upon the necessity for a 

 thorough understanding of the early formative periods in the history 

 of the first -spermatocyte chromosomes. The remarkable feature about 

 the maturation divisions is not, it seems to me, the separation of the 

 chromatids, but rather the means by which they are associated in prep- 

 aration for these divisions. Therefore, objects which present these 

 early stages to the best advantage are the ones which are most likely 

 to give us a proper understanding of tetrad formation and division. 

 Insect material seems to be especially favorable for this purpose, par- 

 ticularly that derived from the Orthoptera and Hemiptera. 



Henking, with others, assumes that because there are twenty-four 

 chromosomes in the spermatogonia and twelve double ones in the first 

 spermatocyte, the latter represent the ones of the earlier generation 

 united end to end. I believe that there is lacking a sufficient proof of 

 this assumption. In this connection, I would call attention to the 

 great difference that exists in the prophases of these germ cells and 

 those of the body cell. In Hippiscus., the chromatin passes the win- 

 ter in the form of the spireme, as it does also in other animals and 



