96 KANSAS UNIVERSITY QUARTERLY. 



chromatids is denominated a chromosome. The objection to this 

 designation has already been stated in the criticism npon the work of 

 Wilcox. 



Vom Rath's criterion of valence is based, not upon the origin of the 

 elements, but rather upon their relation to each other. In deciding 

 as to whether or not the tetrad itself shall be called a chromosome, he 

 makes use of the following reasoning : "Mit grosster Aufmerksamkeit 

 habe ich die Verbindungsfaden zwischen je 4 Chromosomen studiert, 

 aber niemals eine Spur vom chromatischer Substanz wahrgenommen, 

 so dass die 4 Chromosomen jeder Grujjpe als Einzelchromosomen und 

 nicht die Gruppen selbst als Einheiten aufgefasst werden miissen." 

 Just why the presence or absence of chromatic connection should de- 

 termine the nature of a chromosome I cannot see. Suppose, for in- 

 stance, that the chromatids of a tetrad in Gryllotalpa were so closely 

 approximated that they came in contact with each other : would this 

 in any way alter the character of the elements with respect to their 

 origin and ultimate fate '? 



Again, in Hippisciis the chromatids constituting the tetrads are so 

 closely united that their lines of contact are almost invisible. Sup- 

 pose, now, that these were so disposed that they were brought in con- 

 tact only by the interposition of linin threads : would this in any 

 way change the essential character of these elements? There seems 

 to be no reason for believing that it would. The various families of 

 insects have their characteristic habits in the formation of the tetrads, 

 bat they are, in all, essentially the same stnicture, and should not be 

 differently designated on account of these i^eculiarities. 



Concerning the facts recorded by vom Rath in his paper I find 

 few with which to disagree. The main contention I have to make is 

 with regard to the statement concerning which of the divisions cor- 

 responds to the original longitudinal splitting of the thread. It is 

 his evident opinion that the second division completes the separation 

 already inaugurated in the prophase. He says in this connection : 

 ". . . Es kann folglich die eine der beiden Trennungen der 

 Chromosomen auf diese vorzeitige Spaltung des Chromatinfadens 

 zuriickgefuhrt werden, ob dies nun aber die erste oder die zweite 

 Theilung ist, kann nach den Priiparaten nicht mit Sicherheit 

 entschieden werden, ich machte eher an die zweite Theilung denk- 

 en." As in the case of Pyrrhocoris, the evidence presented by 

 the elements during their prophase condition is not conclusive, or, 

 if so, has not been given its true importance. In all respects, the 

 spermatogenesis of Oryllotalpa appears to conform to the typical 

 insect plan. There is no mention made, however, of the occurrence 

 of any such element as the accessory chromosome. I have not had 



