1895 THE MICROSCOPE. 99 



surface, we find (fig. 2), surrounding the edge of the 

 disc, a crown of cillia, thickly implanted, constituting a 

 movable collar, the motions and undulations of which 

 permit the organism to move itself by turning rapidly 

 upon its axis. But these hairs present still another 

 property. Strongly adherent to each other, somewhat 

 in the same way as the barbs of a feather, they act as 

 a circular membrane susceptible of attaching itself to 

 surfaces and of holding itself firmly there. This 

 action is still more easily accomplished because at the 

 very base of the fresh water hydra is a true collar, 

 which much assists them. 



The Trichodine, when it wishes to attach itself, app- 

 lies its membrane and ciliated collar to the surface of 

 the hydra. Then, hollowing the under surface of its 

 disc by voluntary contraction, it trausforms itself into a 

 true cup-glass, comparable to those well-known adhesive 

 candlesticks which one can stick against a glass, or to 

 the proboscis of the octopus. 



But the central part of the contractile disc of the 

 Trichodine does not consist of a simple protoplasmic 

 membrane. We find there a true organism, surpris- 

 ingly well made for a being so low in the scale of ani- 

 mal life. 



Let us press lightly upon the cover-glass of our 

 preparation, in such a manner as to detach some few of 

 the parasites, and let us choose from them one which 

 presents the under surface. 



We find then that this surface is formed of a cup very 

 finely striated, and that its concavity increases or di- 

 minishes according to the contraction of the body. 



In the thickness of the wall of this cup, is a toothed 

 wheel (fig. 2, e) of the greatest delicacy, which sends 

 from the side toward the center some fine radial pro- 

 longations. From the side toward the circumference it 



