124 EDWAKD B. POULTON. 



position of the ovum towards tlie projecting side is against 

 such a theory. The corpora lutea do not seem to be peculiar. 

 The sizes of all structures mentioned can be readily calculated 

 from the figures. Thus there are important distinctions be- 

 tween the Graafian follicles of a Marsupial and those of the 

 higher Mammalia, and yet these distinctions are by no means 

 in the direction of greater simplicity in the former, but rather 

 the reverse. We shall find a very different state of things in 

 Monotremes. 



The Ovary of Monotremata. — Finding such interesting 

 peculiarities in the ovary of Marsupials^ I determined to in- 

 vestigate the same organ in Monotremes. Professor Moseley 

 very kindly allowed me to take the ovary from a female speci- 

 men of Ornithorhynchus, which had been kept in spirits for 

 many years in the University Museum, and also to look over 

 and take what I could from some specimens of Echidna which 

 had been similarly kept, but were not in a favorable con- 

 dition for microscopic investigation. The ovary of Oruitho- 

 rhynchus was flat (it may have been accideutally compressed) 

 and oval, about 13 mm. long, 7 mm. wide^ and 2 mm. thick. 

 The edges were sharp. It was impossible to make out the 

 shape or size of this organ in Echidna. In both cases I treated 

 the organ as previously described after gradual hardening 

 in spirit. Fig. 8x9 gives the appearance of a trans- 

 verse section across the ovary of Ornithorhynchus. The 

 follicles are confined to the edge of the section, and there- 

 fore the surface of the organ. There does not appear to 

 be any distinct arrangement of follicles according to their 

 size, but the small ones always seem to be very near the sur- 

 face. There were indications that the large follicles are con- 

 stricted ofi^, in the presence of a deep furrow encircling some 

 of them. It is probable that this would be far more distinct 

 in the fresh organ. Such constriction is a much more impor- 

 tant character than mere projection, which occurs in Marsu 

 pials, and in some higher orders. There was, of course, no 

 trace of the germinal epithelium, and nothing could be ascer- 

 tained as to the true nature of the stroma. There certainly is 



