66 McCLUXG. 



to show the great probability of the general distribution of the 



structure among insects. 



The published reports of almost all investigators certainly 

 speak very strongly in favor of such a supposition, but in order 

 to assure myself by personal observation that views of such a 

 character were correct, I examined representatives of the different 

 families of the Orthoptera and became convinced that I was 

 right so far. Later, material from the Hemiptera, Neuroptera, 

 Coleoptera, and Lepidoptera was examined only to confirm the 

 opinion that the element in question is a constant character of 

 the insect testicular cells. The recent work of Miss Wallace 

 upon the spider (*oo) would seem to indicate that there is no 

 doubt of its presence in the Arachnids, and with its determination 

 in this class the probability of its general occurrence in the 

 Arthropods is largely increased. I may also say in passing that 

 some hurried examinations of vertebrate spermatocytes lead me 

 to believe that the accessory chromosome is likewise present 

 here. 



If it be conceded that we are dealing with a common element 

 of the sperm-forming cells, it must also be admitted that there 

 exist extensive variations in its appearance and manifestations. 

 To do this, however, is no more than to concede what is known 

 to be true of all other chromosomes so that such an admission 

 can in no way impair the standing of the accessory chromosome 

 as a constant and important nuclear element. It will therefore 

 be understood that the outline history of its behavior in the dif- 

 ferent cell generations, which I intend to give, will apply only in 

 general particulars. Its purpose is more to show the importance 

 of the element than to postulate a type. 



In the spermatogonia, our knowledge of the accessory chro- 

 mosome is due almost entirely to Paulmier and to Sutton. The 

 former author notes in a general way (1 36) that in the meta- 

 phase of the early cell generations there are present two smaller 

 chromatin bodies which, during the breaking down of the sper- 

 matogonial chromosomes to form the spireme, do not suffer any 

 very extensive dissolution. Later these appear as a single body 

 in the prophase of the spermatocyte. Montgomery makes no 

 mention of their behavior earlier than the telophase of the last 



