476 J. BRONTE OATENBY 



with regard to their germ-cells is sure to be of value. I must 

 take this opportunity of thanking Professor J. P. Hill, F.R.S., 

 for allowing me to study his material of Ornithorhynchus, 

 without which I could not have published these notes. 



There is no account extant of the detailed structure of the 

 ovarian egg of Ornithorhynchus, of the yolk formation, of the 

 maturation stages, or of the corpus luteum. Such accounts 

 of the ovary as are published are scrappy and full of errors, 

 this, however, being chiefly due to the scanty and poor material 

 at the disposal of the various observers who have attacked 

 these problems. The material at my disposal, while not having 

 been prepared by the most modern technique, is well preserved 

 by routine methods and allows of a fuller description of various 

 problems than hitherto given. The material consisted of one 

 ovary preserved in Flemming's strong fluid, and of several 

 ovaries preserved by a variety of picric and bichromate fixa- 

 tives. Most of the new results were procured by examination 

 of the Flemming-fixed ovary. 



This work was partly carried out in the Embryological 

 Laboratory, University College, London, and was finished in 

 the Zoological Laboratory, Dublin University. Apart from 

 his kindness in lending me the material, I have to thank 

 Professor J. P. Hill for assisting me by lending some of the 

 literature on Ornithorhynchus and Echidna. 



2. Previous Work on Gametogenesis of Ornitho- 

 rhynchus AND OF Echidna. 



Thirty-seven years ago E. B. Poulton, in his paper on 

 ' The Structures connected with the Ovarian Ovum of Mar- 

 supialia and Monotremata ', gave some account of the general 

 appearance of the ovary and follicle of Ornithorhynchus and 

 Echidna. Poulton's material consisted only of ovaries removed 

 from spirit specimens, and he was consequently much handi- 

 capped. Nevertheless, he succeeded in establishing several 

 facts of great importance. The ovary of Ornithorhynchus, 

 according to Poulton, is flat or compressed, oval, and about 

 13 mm. long, 7 mm. wide, and 2 mm. thick. The follicles are 



