ON THE ANATOMY OF NAUTILUS POMPILIUS. 187 



character of a "germinal vesicle," and the protoplasm first 

 becoming more distinctly aggregated round the nucleus and 

 marked oflf from the surrounding protoplasm and then increas- 

 ing rapidly in size. As the ovum increases in size the substance 

 of the ovarian wall grows up round it to form the follicle, while 

 the syncytium accompanying the ovum apparently gives rise to 

 the lining-cells of the follicle. The latter are pear-shaped 

 structures borne on stalks, which are usually simple, but 

 occasionally branch, thus showing a tendency towards the con- 

 dition in Argonauta, where they are much branched and tree- 

 like. Externally the follicle is covered by a very thin epithe- 

 lium, which distally becomes continuous with the lining layer 

 of "follicle cells" — a layer of thick columnar cells immediately 

 surrounding the eg^. In the young follicle this layer runs 

 concentrically with the outer surface of the epithelium, but as 

 the egg increases in bulk an increase in the surface of this 

 apparently nutritive organ becomes necessary and the follicle- 

 epithelium grows inwards as a series of anastomosing folds. 

 On this account the older eggs when removed from the follicle 

 show on their surface a network of deep fissures formed by the 

 follicular epithelial ingrowths. In the oldest female specimen 

 accessible, unfortunately too macerated to make out many 

 details, the eggs had reached a large size, over 10 mm. in 

 length, and their substance was already enormously yolk-laden, 

 the protoplasm being practically restricted to a small cap on 

 the end of the egg next the follicular opening. Imbedded in 

 this was the large nucleus with densely staining nucleolus. 

 The presence of a definite opening in at least the older follicles 

 and the position of the egg-nucleus close to this, suggest the 

 possibility of fertilization in Nautilus being internal ; and the 

 great size of the eggs and their yolk-laden character point to 

 the segmentation being meroblastic as in other Cephalopoda. 



The wall of the ovary, as of other important organs, is loose 

 and spongy, traversed by extensive blood-sinuses (h.s.). Pro- 

 longations of these pass up the stalks of the follicles, and form 

 a specially developed layer immediately underlying the follicle- 

 epithelium — a condition to be correlated with the provision of 



