THE ACCESSORY CHROMOSOME. 8 I 



very promising field opened up by the work upon artificial par- 

 thenogenesis will throw much light upon these vexed problems. 



LABORATORY OF ZOOLOGY AND HISTOLOGY, 

 UNIVERSITY OF KANSAS, January i, 1901. 



SUPPLEMENT. 



During the period of a year and a half that has elapsed since 

 the completion of the foregoing article, a number of important 

 changes in, and additions to, our knowledge of the accessory 

 chromosome have been made. These are noted in another 

 paper, "The Spermatocyte Divisions of the Locustidae," soon 

 to be published, so that extended reference to them will not be 

 given here. For the sake of completeness, however, I deem it 

 proper to make brief mention of such as affect the main points 

 of this contribution. 



First, I may observe that the exact character of the unequal divi- 

 sion of the accessory chromosome in the spermatocytes of the 

 Orthoptera has been established. As may be noted in Tf 42, I 

 could not determine the behavior of this element in Xiphidium 

 with certainty. From its absence in large numbers of spermatids, 

 though, I was inclined to support Henking's view that it remained 

 undivided in one of the spermatocytes. In other genera of 

 Locustidse, OrcJiesticus, Anabrus, Microcentrum, and Scudderia, 

 I have since been able to demonstrate with certainty that the 

 accessory chromosome divides but once in the spermatocytes. 

 Here, unlike Pyrrlwcoris, the second spermatocyte mitosis wit- 

 nesses the separation of the chromatids of the accessory chromo- 

 some. The end result is, nevertheless, the same in each case. 



Further confirmation of the fact may be found in the work of 

 R. de Sinety upon other species of Orthoptera, in which he re- 

 cords exactly similar processes. I feel safe in stating it as estab- 

 lished therefore, that in the Orthoptera and in the Hemiptera 

 the accessory chromosome is normally present in exactly one 

 half the spermatozoa. 



With regard to the general distribution of the accessory chro- 

 mosome, I may state that a student in this laboratory, Mr. M. 

 W. Blackman, has been able to demonstrate its presence in the 

 Myriapoda where it evinces, in connection with all the other cell 



