10 . THE VICTORIAK NATURALIST. 



trated by diagrams and preparations. The following is an ^ 

 abstract : — 



" The edible mussel, so common on our coasts, and occasion- 

 ally sold on the streets of Melbourne, is naturally fixed to some 

 object by means of a tuft of strong, silky hairs, called its beard, 

 or byssus. But, although thus naturally anchored, it may, on 

 an emergency, move about a little. It has been observed to 

 move both with and without its shell, and perhaps stranger 

 still, if certain parts are detached from it, they, too, move 

 about in various ways. The entire mussel has been seen to 

 crawl up the sides of a glass vessel to the extent of three inches 

 in a single night ; and without its shell it moves in a rotatory 

 manner. This latter movement is due to innumerable delicate, 

 microscopic, hair-like filaments, called cilia, which covsr 

 various parts of the body. Portions of the body, when cut 

 off, might naturally be thought to be dead and incapable 

 of movement, but here large and important portions exhibit 

 movement, when free to do so. Of these moving detached 

 parts the principal are the mantle, which covers the 

 body, as with a cloak ; the gills, which hang down 

 by its side ; the so-called foot — a little, fleshy, tongue- 

 shaped body on the under-surface ; and two triangular flaps on 

 each side of the mouth, called labial palps. Each part has its 

 own peculiar mode of motion, and some can stop and start 

 again, can reverse the direction of movement and resume the 

 original, and can even back out from obstacles when meeting 

 with them in their path. The nature of the movement is usually 

 either rotatory or translatory, or both combined. When rotatory 

 the direction may either be the same as that of the hands of a 

 watch or the reverse. The rate of rotation is variable. An average 

 of 50 rounds gave 5 minutes per round, and the quickest was per- 

 formed in i^ minutes. The rate of forward movement is like- 

 wise variable. It may be as slow as an inch in 4- days for the 

 foot, or as quick as an inch in 2 minutes for the gill. The 

 quickest recorded for the gill was at the rate of an inch a 

 minute, or 44 days per mile. 



"In the case of the gills they can move when placed either 

 horizontally, vertically, or when turned upside down. Their 

 vertical movement may average i inch in 10 minutes. 



"As to the duration of this power of movement, it has been 

 known to last for at least 8 days. The iact that parts can 

 move at all when detached from the body is sufficiently interest- 

 ing, but that they do so in a definite manner and direction, 

 even sometimes exhibiting a certain amount of will-power, 

 increases the wonder. And while these movements throw new 

 light on the uses of the parts concerned, they are not without 

 some practical bearings on parts of our own bodies, for the 

 lining membrane of the nose and of the windpipe, for instance. 



