184 W. E. AGAR 



Y-chromosomes in the Mammalia — first clearly established by 

 Painter (1922) in Didelphys. In Macropus this element 

 is very minute, and, though I had shown it in several figures, 

 I failed to interpret it properly until we received Painter's 

 paper, which arrived at a moment when Mr. Greenwood (whose 

 results are to be published in this journal) was paying attention 

 to a very minute chromatic body occurring in several other 

 species of Marsupials at which he was working. It imme- 

 diately became apparent that this body was the Y-chromosome. 

 Comparison with his work, and with Painter's description of 

 Didelphys, quickly established that the small body already 

 observed in Macropus is also a Y-chromosome. 



It is a pleasure to acknowledge my indebtedness to several 

 people for assistance in obtaining this material. Dr. T. L. 

 Bancroft, of Eidsvold, Queensland, has sent me in the last two 

 years a great number of specially'' preserved testes of Marsupials, 

 Monotremes, Ceratodus, and many other Australian animals. 

 For living material utilized in the present paper I have to 

 thank Dr. Colin MacKenzie, Director of the Australian Institute 

 of Anatomical Eesearch, and Mr. W. H. D. Le Souef, of the 

 Zoological Gardens, Melbourne. 



Material and Methods. 



The two species dealt with in the present communication 

 are Macropus ualabatus and Petauroides volans. 

 These genera belong respectively to the Diprotodont families 

 Macropodidae and Phalangeridae. 



The material was mostly preserved in Flemming, Bouin, and 

 Allen's modification of Bouin (1913, 1915). I have found the 

 latter method excellent, especially when followed, as Allen 

 recommends, by anilin and bergamot oils in place of the higher 

 alcohols and xylol. For general purposes I have found this 

 method the best I have yet tried for mammals. 



The standard stain used was Heidenhain's iron haematoxylin, 

 though safranin, methyl green, and acid fuchsin, and others, 

 were used as controls. 



As in former work, I have found thick sections much more 



