M'CLUNG : SPERMATOCYTE DIVISIONS OF THE ACRIDID/E. 93 



central chromosomes of Fig. 145 by Montgomery and Fig. loa of this 

 paper. 



It affords me great pleasure, after having had to differ so much 

 from Montgomery in other matters, to confirm his belief in the origin 

 of the accessory chromosome. As already described, it arises in Hip- 

 piscus and other AcrididtB, as it does in Euchisius, from one of the 

 spermatogonial chromosomes which does not become reticulated and 

 joined with the substance of the others to form the spireme. In the 

 Locustidte, as previously stated, I have not been able to satisfy myself 

 that the element has just this origin. On the other hand, I have no 

 proof that it does not thus arise. Further comparative study, now 

 begun, will doubtless make this point clear. 



I have already stated that my studies upon insect spermatogenesis 

 have led me to believe that the processes of spermatocyte divisions are 

 essentially the same throughout the class Insecta. I must, therefore, 

 disagree with the conclusions reached by Henking (5) from a study 

 upon Pyrrhocoris apterus. According to this author, the twenty-four 

 chromosomes, characteristic of the spermatogonia, appear in the first 

 spermatocyte, but. instead of being single, are united by pairs. The 

 result of this is that an equatorial view of a spermatogonial metaphase 

 will show a plate of simple, round chromosomes ( twenty-four in num- 

 ber from a polar view ) ; while, on the contrary, a chromatic plate of 

 the first spermatocyte shows the chromosomes to be dumb-bell shape, 

 and arranged as a double plate, which, viewed from the pole, exhibits 

 twelve chromosomes. 



In reaching this conclusion, Henking disregards, or rather misin- 

 terprets, certain significant figures of the late prophases. I refer to 

 those represented in his Fig. 20, which he mentions as "die mit vier 

 Verdickungen versehenen Ringe." Instead of considering these nor- 

 mal structures, he regards them as transformation stages, or accidental 

 unions, of simpler elements. 



Henking's error consists in regarding the elements of the first 

 spermatocyte division as double instead of quadruple — a mistake 

 which would easily be made if the fully formed structures were ex- 

 amined instead of those in the preliminary stages. The true difficulty 

 is recognized by vom Rath when he says: "Ich erinnere daran, dass 

 audi bei Gryllotalpa bei den beiden letzten Theilungen stets 2 

 Chromosomen einander genahert sind und ein Paar bildeii, bei 

 Pyrrhocoris konnte eine noch weiter gehende Vereinigung eines 

 Chromosomen-Paares bis zu einer scheinbaren Verschmelzung statt- 

 gefunden haben." As in IPippiseus, the cliromatids are closely 

 united, so that the lines of separation are quite invisible. Particularly 

 would this be true of cells where the elements are so small as they 



