author's abstract of this paper issued 

 by the bibliographic service, december 12 



STUDIES IN MAMMALIAN SPERMATOGENESIS 



I. THE SPERMATOGENESIS OF THE OPOSSUM (dIDELPHYS 



virginiana)^ 



THEOPHILUS S. PAINTER 



EIGHT TEXT FIGURES AND THREE PLATES (tWEXTY FIGURES) 



INTRODUCTION 



The opossum, along with many other mammals, is a form for 

 which the diploid or somatic chromosome number is a matter in 

 dispute. In 1911 Jordan gave an account of the spermatogenesis 

 of this animal. His results as they touch the chromosomes are 

 briefly as follows: 17 chromosomes were found in dividing sper- 

 matogonia; in the primary spermatocytes 9 chromosomes were 

 present — one of these was bipartite in form and passed apparently 

 undivided to one pole of the spindle; in part of the second sper- 

 matocytes this bipartite element was found, in others it was 

 lacking. Because of its behavior and distribution, Jordon inter- 

 preted this bipartite chromosome as the true sex-chromosome, 

 and from his description it is clear that one half of the sperm 

 carry this element and one half lack it; in other words, that the 

 male opossum possessed the X-0 type of sex-chromosome. No 

 further work upon the male opossum has appeared except a short 

 note by the author (Science, May 27, 1921) in which the main 

 results of this paper were outlined. 



Recently, Hartman ('19) working upon the early stages of 

 opossum embryos, reports that in the ova (polar-body spindles) 

 he finds from 10 to 12 chromosomes. Since 12 chromosomes are 

 found in several spindles where the chromosomes are most favor- 

 ably placed for counting, Hartman concludes that this is the 

 true reduced or haploid number. From this it would follow of 



' Contribution no. 150, from the Department of Zoology, University of Texas, 

 Austin, Texas. 



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