80 PROGRESS OF MICROSCOPICAL SCIENCE. 



The second layer, like the first, is composed of medullatcd fasciculi, 

 of smaller size, freely intercommunicating with each other, and lying 

 immediately beneath the capillaries. The third layer is composed of 

 still finer meduUated fasciculi, and is on a level with the capillaries. 

 Small fasciculi of this layer, composed of from two to four fibres, run 

 to hair follicles, and, having encircled each with one or several turns, 

 terminate in a little nervous coil, knot, or glomerulus at its base. 

 The nerve knots are almost perfectly spherical, with a diameter of 

 about 0*015 of a millimetre ; and they occasionally include a few 

 ganglion cells in their interior. Schobl estimates the number of 

 nerve knots at about 12,000 for each ear. Finally, from the last- 

 named nerve plexus a fourth plexus arises, which is composed of pale 

 fibres, and which lies immediately beneath the Malpighian layer. At 

 their points of junction are well-marked nodal enlargements. The 

 plates are exquisitely done, but we fear that their artistic merits are 

 higher than their value as fair observations. 



Experiments with Vibrating Cilia. — A very curious set of experi- 

 ments on this subject is described by Professor Jeffries Wyman, M.D. 

 They appeared in the 'American Naturalist' as long ago as last 

 October, but we have not had space to name them. They are cer- 

 tainly very curious and interesting, and are so well described that 

 our readers will have no difficulty in carrying them out. The first- 

 described experiments are those made in water. For these the gills 

 of Uuios and Anodontas are well suited. Their cilia are quite active, 

 and vibrate in such directions, that on the inner gill the motion is 

 from the free edge, and on the outer to it, facts which the experimenter 

 should keep in mind. If an inner gill is cut away from its attach- 

 ment and laid on the bottom of a flat dish, its cilia acting as legs, it 

 will soon begin to move with its free edge forwards, and will in the 

 course of time travel the entire length of the dish. Prof. Wyman has 

 seen a whole gill move ten inches in four houi's. Under similar 

 circumstances the outer gill will move with its base or cut edge 

 forwards. This difference depends, as will be readily seen, upon the 

 fact that the cilia of the two gills vibrate in opposite directions. 

 The result of ten experiments gave the rate of motion of a piece of gill 

 measuring 12 mm. by 14 mm., 6 mm. a minute. If two outer gills are 

 laid with their free edges towards each other they will at once begin 

 to approach, and it frequently happens after meeting that one crawls 

 directly over the other. Another and more striking experiment 

 which shows the reaction of cilia on each other may be made as 

 follows. Fasten a gill to a piece of cork under water, and place upon 

 it a portion of a second gill about a half-inch square. If this piece is 

 so placed that the cilia vibrate in the same direction with those of the 

 gill below, it will remain stationary, or nearly so, since the cilia offer 

 no resistance to each other. If now the upper piece is reversed so 

 that the cilia vibrate in opposite directions, the upper piece will move 

 with double the speed and through twice the distance in a given time 

 that it would with its own cilia alone, for while the lower cilia move 

 the upper piece through a certain space, the cilia of the upper piece 

 also move this in addition through an equal space. A third form of 



