A PECULIAR NUCLEAR ELEMENT IN THE MALE 

 REPRODUCTIVE CELLS OF INSECTS. 



C. E. McCLUNG. 



In working out the spermatogenesis of one of the Locustidae, 

 XiphidUim fasciatmn, a nuclear element not heretofore described 

 arrested the attention of the writer, and will here be given pre- 

 liminary notice in order that other investigators in the same 

 line of work may be induced to look for it in their preparations. 

 For the sake of convenience this structure will be called, 

 provisionally, an accessory chromosome. 



While but the one species has been studied and the appear- 

 ance of the new element noted, a study of figures representing 

 insect spermatogenesis indicates that it is not merely a specific 

 character. Such an inspection of the figures given by different 

 writers shows clearly that the body under discussion has been 

 observed, but that its true character has not been recognized. 

 The reason for this may be apparent later, when the changes 

 it undergoes have been described. The truly remarkable and 

 striking nature of the element and its obvious importance in 

 the formation of the spermatozoon render a more thorough 

 knowledge of it highly desirable. 



In order to make clear the true character of the body, an 

 account of its behavior in different stages of the maturation of 

 the spermatozoon will be given, and then attention will be 

 called to the most striking features distinguishing it. 



As it first appears in the spermatogonia of Xiphidium 

 fasciatum, there would be no hesitation in calling it a nucleolus 

 except for its unusual situation on the surface of the nuclear 

 vesicle. It is a small, irregularly rounded body, and lies imme- 

 diately under the nuclear membrane (Fig. i). Before the 

 division figure is established, however, it takes on the form of 

 a thread which becomes "U "-shaped (Fig. 2). Still further 

 contraction ensues, and by the time of the metaphase the 



