4 PHILOSOPHICAL TIIANSACTIONS. [aNNO 1785. 



tentacula at the bases of the cones having just room enough to move without 

 touching each other. The thin membrane which lay between the cones and the 

 inclosing shell is protruded in the form of a fold, and lies over the external shell 

 which projects from the brain-stone. 



The membranes have a slow spiral motion, which continues during the whole 

 time of their being expanded; and the tentacula on their edges are in constant 

 action. The motion of the membrane of the one cone seems to be a little dif- 

 ferent from that of the other, and they change from the one kind of motion to 

 the other alternately, a variation in the colour of the membrane at the same 

 time taking place, either becoming a shade lighter or darker ; and ihis change 

 in the colour, while the whole is in motion, produces a pleasing effect, and is 

 most striking when the sun is very bright. The membranes however at some 

 particular times appear to be of the same colour. While the membranes are in 

 motion, a little mucus is often separated from the tentacula at the point of the 

 cone. On the least motion being given to the water, the cones are immediately, 

 and very suddenly, drawn in. This apparatus for catching food is the most deli- 

 cate and complicated that he had seen. He annexed 2 drawings of the animal 

 in its two different states, one in search of food, and one while lying at rest. 



Mr. Hunter s Postscript. — Animals which come from foreign countries, and 

 which cannot be brought to England alive, must be kept in spirits to preserve 

 them from putrefaction, which makes them less fitted for anatomical examina- 

 tion ; for the spirits, which preserve them, produce a change in many of their 

 properties, and alter the natural colours, and texture of the parts, so that often 

 the structure alone of the animal can be ascertained ; and where this is not 

 naturally distinct, it becomes often quite obscured, and the texture of the finer 

 parts is wholly destroyed, requiring a very extensive knowledge of such parts in 

 animals at large, to assist us in bringing them to light : this happens to be the 

 case with the animal whose dissection is the subject of this postscript. 



The animal may be said to consist of a fleshy covering, a stomach and intes- 

 tinal canal, and the two cones with their tentacula and moveable shell, which 

 last may be considered as appendages. The body of the animal is flattened, and 

 terminates in two edges, which are intersected by rugae, the fasciculi of trans- 

 verse muscular fibres which run across the back being continued over them. 

 On each of these edges is placed a row of fine hairs, which project to some dis- 

 tance from the skin. The fleshy covering consists principally of muscular fibres: 

 those on the back are placed transversely, to contract the body laterally ; those 

 on the belly longitudinally, to shorten the animal when stretched out, and to 

 draw it into the shell. The stomach and intestine make one straight canal : the 

 anterior end of this forms the mouth, which opens into the grooves made by the 

 spiral turns of the tentacula round the stem of each of the cones; and the in- 



