120 EDWAKD B. POULTON. 



above. But important differences exist between the Marsupial 

 Graafian follicles and those hitherto considered universal 

 among mammalia. Thus even in the lowly-magnified (fig. 1) 

 the larger follicles are seen to possess a very thin and regular 

 membrana granulosa, and the ovum in a (probably) full-sized 

 follicle does not lie in a cumulus proligerus, but is embedded 

 in a substance corresponding in' position with the liquor folli- 

 culi. Minute examination sliows further peculiarities. The 

 young follicles appear to be normal ; the ova are at first sur- 

 rounded by a single layer of flattened cells — the follicular epithe- 

 lium. These thicken and then multiply, forming a membrana 

 granulosa several cells deep. It is then noticeable that the 

 cells in immediate proximity to the ovum are not columnar, 

 and thus the layer of radiating cells round the ovum, so cha- 

 racteristic of the higher mammalia, is entirely absent. In fact_, 

 these cells show a tendency towards the flattened shape, and 

 columnar cells never appear in this position throughout the 

 further stages of the follicle. 



The granulosa cells have distinct readily-staining nuclei; 

 they are very easily changed in shape, and it is hard to dis- 

 tinguish their outlines. They are probably polyhedral^ with a 

 frequent tendency to be drawn out parallel with the side of 

 the ovum. The layer round the ovum sometimes shows a ten- 

 dency to split away from the others. There is sometimes an 

 indication of columnar structure in the cells near to the folli- 

 cular wall. The great want of persistence in form shown by 

 these cells is seen when the granulosa has split away from the 

 follicular walls (as very frequently happens). Then the cells 

 are drawn out into long threadlike processes, of which many 

 are left behind, fixed to the membrana propria. The latter is 

 extremely thin. Subsequent examination of a fresh specimen, 

 and after the use of other reagents, confirms the above de- 

 scription. The outer granulosa cells are columnar, the others 

 polyhedral. The outlines are much more distinct than in the 

 figures which were drawn from the organ hardened in chromic 

 acid. 



The zona pellucida (?) is excessively thin throughout the 



