THE SPERMATOGENESIS OF THE MONGOOSE ; AND A FURTHER COM- 

 PARATIVE STUDY OF MAMMALIAN SPERMATOGENESIS, WITH 

 SPECIAL REFERENCE TO SEX CHROMOSOMES. 



By H. E. Jordan. 



INTRODUCTORY. 



In view of the recent discovery of heterochromosomes in a number of 

 the higher vertebrates it seemed desirable that the spermatogenesis of still 

 other forms should be carefully studied with particular attention to the 

 possible presence and variable behavior of homologous "accessory" chro- 

 mosomal elements. While this study was in process opportunity was 

 afforded to collect in Jamaica, British West Indies, material of the mon- 

 goose.^ This material is interesting in a number of respects and serves 

 well as a starting-point for such comparative study as will appear from its 

 description. Other material at hand includes that of cat, squirrel, pig, 

 rabbit, white mouse, sheep, horse, mule, bull, and dog. 



HETEROCHROMOSOMES LACKING IN MALE. 

 MONGOOSE. 



Spermatogonial nuclei more generally contain three plasmosomes 

 (fig. i), though there may be more or fewer. Only a very few nuclei were 

 seen in mitosis. Many stages of apparent amitosis are present (fig. 2). 

 The rarity of mitotic figures and of binucleate cells indicates that the pre- 

 vailing type of division among the spermatogonia is amitotic. The presence, 

 however, of a few binucleate spermatocytes and spermatids shows that 

 cell-body divisions do not always follow the nuclear divisions. 



The primary spermatocytes contain a single nucleolus (plasmosome), 

 seen only in the resting condition of the nucleus. The fact that this body 

 never appears subsequently makes the synapsis and division stages of the 

 mongoose especially favorable for study with reference to the presence of 

 an "accessory chromosome." There can be no confusion here between a 

 plasmosome and a chromosome-nucleolus, as has apparently been the case 

 in some forms. Moreover, the early disappearance of the plasmosome in 

 mongoose gives support to the general conclusion that synaptic and post- 

 synaptic chromatin elements are chromosomes, more especially when 

 invariably on the nuclear membrane instead of being disposed at random. 



The synizesis phase is characterized by a very compact, deeply chro- 

 matic mass of simple threads (fig. 4). The mass is situated at the pole of 



» This opportunity occurred during a month's stay at the temporary Marine Biological Laboratory of the 

 Carnegie Institution of Washington at Montego Bay In the spring of 1912. I take this occasion to express 

 my thanks for the privileges of the Institution's expedition to Jamaica, and for daily kindnesses on the part of 

 the director, Dr. Alfred G. Mayer. 



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