space covered by the ears a few eyes are present. In all there 

 are frequently as many as one hundred on each of the lobes of 

 the mantle. Their size even in old individuals is noticeably 

 unequal and they are not arranged in any order of size. As 

 there are many more eyes in large than in small individuals, new 

 ones must be added during the growth of the animal and their 

 size may be an indication of their age. If this is true, new eyes 

 are not added in accordance with any plan but make their 

 appearance as spaces for them occur. The outer ends of the 

 stalks on which the eyes are set are deeply pigmented with black 

 or brown pigment, and the eyes themselves are blue and exceed- 

 ingly brilliant. The structure of the eyes will be considered 

 under the head of sense organs. 



The mantle margins, including the infolded ridges and ten- 

 tacles, are usually highly pigmented. Yellow and brown, either 

 light or so dark as to approach black, are conspicuous in this 

 pigmentation. Sometimes the margins are nearly of the same 

 color throughout their extent but they are frequently blotched 

 with different colors and with different shades of the same color 

 arranged in irregular patterns so that with the infolded ridges, 

 the tentacles and the brilliant eyes, the margins make very strik- 

 ing objects. What purpose the brilliant pigmentation may 

 serve I cannot say. Perhaps they are not as conspicuous among 

 the yellow incrusting sponges and the other variously colored 

 incrusting growths among which they live. Living in deep 

 water as the animal does, these are matters that are not easily 

 studied. 



The distribution of nerves and blood vessels in the mantle will 

 be described in the general consideration of the nervous system 

 and the vascular system of the animal. 



VISCERAL MASS AND FOOT. 



It will hardly be necessary to describe the general shape and 

 positions of these portions of the animal as reference to figures 

 will make the relation of parts much clearer than description 

 (figs, ii and 12). It will be noticed that the portion containing 

 the digestive gland or liver, and the reproductive portion of the 

 viscera are not broadly connected, and that the foot is placed 

 anterior to the heart and ventral to the connecting portion. 



16 



