The Male Meiotic Phase in two Genera of 

 Marsupials (Macropus and Petauroides). 



By 

 W. E. Agar, F.R.S., 



Professor of Zoology in the University of Melbourne. 



With Plates 12-14. 



A VERY slight experience of cytological research is sufficient 

 to impress the worker in this field with the different facilities 

 for accurate research afforded by different organisms, and also 

 with the importance of discovering the most favourable objects 

 for such research. Consequently I have been making a cyto- 

 logical survey of such groups of Australian animals as seemed 

 most likely to afford useful cytological material, paying at 

 first particular attention to the Marsupials, for two reasons. 

 The first is the well-known technical difficulties presented by the 

 Eutherian mammals on account of the usually rather large 

 number and tendency to clump of their chromosomes, and the 

 second is that Jordan's work on the American opossum (1911) 

 showed that in this marsupial the number of chromosomes is 

 comparatively small. Jordan determined the number as seven- 

 teen (male), but Painter (1922) has raised it to twenty-two. 

 Up to the present we have made in this laboratory a pre- 

 liminary survey of some fourteen species of Marsupials, and 

 this paper presents an account of the more important features 

 of two of these which have been worked out in more detail. 



At present the most interesting feature of this work is 

 undoubtedly the determination of the conditions of the sex 

 chromosomes, a problem which has always presented in 

 mammals considerable elements of dubiety. Of primary 

 importance is probably the confirmation of the occurrence of 



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