CEPHALOPODA. 193 



is concentric with the plug. Definite layers cannot be made out, but portions of 

 greater and less density alternate with each other (tigs. 12, 13, ///.). In some instances 

 I was able to make out a nucleus either in the plug itself or in the subjacent granular 

 tissue. This spheroidal mass lias no definite boundary, but gradually passes over into 

 the connective-tissue lying beneath the epithelium. 



The epithelium covering the surface of the papilla undergoes a modification in the 

 neighbourhood of these organs. For a little distance around, the cells become 

 columnar instead of cubical, and their nuclei long and attenuated instead of 

 spheroidal (compare figs. 11 and 13). It seems probable that this is due to a 

 compression caused by the plug pushing its way to the surface from beneath. The 

 cells closely surrounding the plug are even more flattened, so as to form an envelope 

 round the sides of the plug, and often to extend inwards a little way below the 

 general lower surface of the epithelium (fig. 9), so that a section parallel with the 

 surface shows them as a ring surrounding the plug, and in their turn encircled by the 

 granular mass (fig. 12, ep.). 



The upper surface of the plug shows a dense deeply stained boundary, outside which 

 is sometimes a thicker more faintly stained layer (fig. 10), and from this arises a bunch 

 of radiating fibres (figs. 10, 11, f.). These are extremely thin, straight, and many 

 of them have slight swellings at the end. They are about 0*06 millim. in length, and 

 their diameter too small to be measured by any appliances at my disposal ; it is 

 certainly less than 0'0015 millim. Generally they appear quite discrete, but in one 

 section there seemed to be a delicate transparent substance connecting their tips, 

 and spreading out beyond their extremities into a sort of thin cloud. I did not 

 observe this in any other sections and conclude that it is in some way due to artificial 

 causes. 



It is only some half-dozen of these organs which present the appearance just 

 described, that is to say, which come up to the surface and give off a tuft of fibrils. 

 The remainder are completely covered by the epithelium, and hence I conclude they 

 are similar bodies in course of development, which have not yet reached the surface. 



The nature of these bodies seems to me very obscure ; the different possibilities are 

 as follows : In the first place they may be parasitic ; the radiating tuft of fibrils with 

 thickened ends suggests an Acinetan, but against this are to be set the following 

 considerations : these bodies appear to originate from within and not from without, 

 there is no definite boundary between them and the surrounding connective-tissue, 

 and their granular substance does not resemble the cell contents of the Protozoa. 



Assuming that they belong to the Cephalopod, there seem to be difficulties in the 

 way of referring them to any recognised type. The possibility of their being either 

 glandular or phosphorescent seems to be excluded by the tuft of radiating fibrils, whilst 

 against a sensory function must be urged the fusion of their lower portion with the 

 surrounding tissues and the fact that no nerves have yet been traced to them. On 

 the whole, this last view would seem to present less difficulty than the others, and it 



2 c 



