4 J. P. HILL. 



abnormal). There can he little doubt that Dasyurus, like 

 various other Marsupials (e.g. Perameles, Macropus, etc.), 

 has suffered a progressive reduction in the number of young- 

 reared, but even making due allowance for that, the excess 

 in production oF ova over requirements would still be remark- 

 able enough. Whether this over-production is to be correlated 

 in an}' wiiy with the occurrence oi^ abnorinalities during early 

 development or not, the fact remains that cleav;i,ge abnor- 

 malities are quite frequently met with in Dasynrus. 



Technique. — As fixatives, I have employed for ovaries 

 the fluids of Hermann, Fieinming, Ohhnacher, and Zenkei-; 

 for ova and early blastocysts, Hermann, Flemmiug, Perenyi, 

 and especially picro-nitro-osmic acid (picro-nitric acid [Mayer] 

 96 c.c, 1 per cent, osmic acid 2 c.c, glac. acetic acid 2 c.c.) ; 

 for later blastocysts, the last-named fluid especially, also 

 picro-corrosive-acetic and corrosive-acetic. 



To facilitate the handling of ova and early blastocysts 

 durinj>- embeddin":, I found it convenient to attach each 

 specimen separately to a small square of pig's foetal membrane 

 by means of a dilute solution of photoxylin (1 to 2 per cent.). 

 Orientation of the specimen was then easily effected during 

 final embedding, under the low power of the microscope. The 

 larger blastocysts were double-embedded in photoxylin and 

 ])araffin, the cavity of the blastocyst being tensely filled with 

 the photoxjdin solution by means of a hypodermic syringe 

 fitted with a fine needle. 



For the staining of sections, Heidenhain's irou-hiema- 

 toxylin method proved the most satisfactory, and was almost 

 exclusively employed. Entire portions of the blastocyst wall 

 were stained either with Ehrlich's or Delafield's hasmatoxylin. 



I am much indebted to Mr. L. Schaeffer, of the Anatomical 

 Department of the University of Sydney, and to Mr. F. 

 Pittock, of the Zoological Department, University College, 

 for invaluable assistance in the preparation of the photo- 

 micrographs reproduced on Plates 1-5, and also to Mr. A. 

 Cronin, of Sydney, and Miss M. Rhodes, for the drawings 

 from their respective pencils reproduced on Plates 6 and 7. 



