285 



What this "chromatin nucleolus" as first described by Henking ('90) 

 in Pyrrhocoris apterus, and as found typically in Orthoptera and here 

 designated the accessory chromosome (Mc Clung, '02) may ultimately 

 mean in relation to inheritance and sex — whether a sex-determinant as 

 proposed by Mc Clung; or perhaps representing sex characters, sex 

 itself being determined by protoplasmic conditions external to the 

 chromosomes as suggested by Wilson; or merely a structure associated 

 with the cause of sex as suggested by Bateson ; or again being a sex- 

 determinant only by virtue of a difierence in activity or amount of 

 chromatin and thus simply the morphological expression of a hidden 

 physiological cause as also suggested by Wilson — this investigation 

 does not presume to unfold nor does it hope to even illuminate the 

 problem. Its only object is to present the history of this odd element 

 from its first origin in the secondary spermatogonia through its various 

 changes during the growth and maturation processes to its final dis- 

 appearance in the head of the ripening spermatozoa in the orthopteran 

 form, Aplopus Mayeri. Theoretical considerations, as also an account 

 of the earlier and later stages of spermatogenesis, are reserved for 

 a later paper which will appear elsewhere. 



The material upon which this investigation is based was obtained 

 through the kindness of Dr. Alfred G. Mayer, Director of the Tor- 

 tugas Laboratory of the Carnegie Institution of Washington, from Log- 

 gerhead Key, Florida. The material was preserved in Flemming's 

 strong solution and in sublimate acetic. Both methods of fixation yielded 

 uniformly admirable results. The sections were cut at 6| micra, and 

 stained with Heidenhain's iron hematoxylin method with and without 

 counterstain. Sections stained with methyl green and with thionin con- 

 firmed in every detail the results obtained by the hematoxylin stain. 



The primary spermatogonia in the resting stage present a pale- 

 staining nuclear reticulum (Fig. 1) with occasional karyosomes. The 

 amount of cytoplasm is very sparse. Nothing resembling an accessory 

 chromosome or even a plasmosome can be detected. Division is usu- 

 ally by mitosis but amitotic divisions do occur. Such amitoses are 

 frequently not consummated in complete cell division. A binucleate 

 cell results which after later mitoses gives rise to spermatocytes of 

 double the number of post-reduction chromosomes (36) and these in 

 turn to giant spermatids (Fig. 47) and non- functional spermatozoa. 

 The chromosome complex of the metaphase stage numbers 35 (Fig. 2). 

 None of these chromosomes can be identified as the future accessory 

 or "odd chromosome" (Stevens, '05). Secondary spermatogonia (Fig. 3) 

 can be distinguished from the primary by their arrangement in cysts 



