360 Proceedings of the Royal Physical Society. 



this network, which, as shown in the figure, are not of 

 uniform size, but vary somewhat, enclose the yolk " cells ; " 

 the latter are aggregations of minute spherules, or consist of a 

 single drop of fat which occupies the whole space. Interme- 

 diate stashes between these two conditions are observable as 

 may be seen from the figure, and also from Fig. 5, which repre- 

 sents a portion of the network much more highly magnified. 



The section, of which Fig. 7 is an illustration, was one of 

 a fortunately complete series through a large ovum rather 

 more tlian 1 mm. in diameter ; I have been able therefore to 

 note the structure and position of the germinal vesicle. In 

 my sections the germinal vesicle {g.v) was conspicuous through 

 having been well stained by the Borax carmine ; it is situated 

 eccentrically apparently at the junction of the peripheral 

 homogeneous part of the yolk with the central portion, 

 but chiefly in the latter ; it is bounded by a distinct 

 membrane; the germinal spot {g.s) was also conspicuous, 

 and situated again eccentrically within the germinal vesicle. 

 The substance of which the germinal vesicle is composed has 

 the appearance of a fluid or semifluid material, which has be- 

 come coagulated by the re-agents used in the hardening of the 

 tissue. I could see no network; the outer part of the germinal 

 vesicle was rather more deeply stained than the inner portion. 



The largest ovarian ova of Echidna, measuring up to three 

 millimetres in diameter, appeared to consist of hardly anything 

 more than a mass of yolk spherules closely aggregated to- 

 gether, so much so that in many cases they had become more 

 or less hexagonal owing to mutual pressure. The size of the 

 yolk granules varies pretty considerably, and the accompany- 

 ing figure (PL XVIL, Fig. 4), which represents a portion only 

 of such an ovum as that which is at present being described, 

 illustrates this point : a, are the larger granules, which are 

 generally circular, but in some cases have assumed an 

 angular contour through pressure ; among these may be seen 

 a number of smaller granules (h) ; here and there is an area 

 distinguished by being composed of only small granules ; the 

 yolk spherules have in part fused together to form largish 

 irregular- shaped masses (c), but this may easily be a post- 

 mortem chanjze. 



