510 



Suppose, however, for the sake of argument that we allow the 

 assumption that a cilium is composed of an axis which plays the part 

 of an endo-skeleton and of a soft contractile plasma which is not only 

 supported by but even takes a purchase from it, as the muscles do 

 from the bones of the vertebrate limbs: Has Dr. Pütter or any 

 other physiologist, who may have adopted and perhaps taught this 

 theory as a reasonable explanation of the mode of action of cilia, formed 

 any conception of the rigidity combined with elasticity which such a 

 skeletal rod must necessarily possess in order not only to overcome 

 the very considerable resistances which the cilia are competent to deal 

 with — and we know from Bowditch's experiments that a weight 

 thousands of times greater than the total mass of the cilia upon which 

 it rests can yet be easily moved by them — but even to move the 

 cilia themselves through water or the far more viscous fluid in which 

 many cilia work? I venture to repeat what I have already stated 

 that a rod of this tenuity if it had the rigidity and elasticity of 

 steel would be entirely insufficient to overcome the resistance of 

 the fluid alone. Therefore, in order to support his theory, it is ne- 

 cessary for Dr. Pütter to assume a hypothetical material for his axis 

 which shall far exceed even steel in those properties. But Dr. Pütter 

 has already stated that his axial skeleton is only protoplasm (!) which 

 can at the most be described as semi-fluid, without solidity and cer- 

 tainly without rigidity. I defy any ordinary mind to conceive how 

 such a material can play the part of an endo - skeleton ! Even if we 

 could conceive such an endo-skeleton as being bent over by the action 

 of a "contractile substance" outside it, it is physically inconceivable 

 that a filament so soft and of such tenuity as a cilium should have 

 any power by such means even to move its own mass through a 

 watery fluid, still less to push before it solid objects infinitely exceeding 

 itself in bulk and weight. And it is in the highest degree improbable 

 that such primitive protrusions of protoplasm should from their first 

 appearance be differentiated in the manner which is assumed by Dr. 

 Putter's theory. But all such difficulties disappear on the assumption 

 that hydraulic pressure produced by the ebb and flow of fluid is the 

 moving cause of the phenomenon. The character of the movement, 

 the manner in which the cilia curve round in the direction of the 

 stroke in spite of the resistance of the fluid within which they move, 

 the relatively great force which accompanies the movement, the analogy 

 of the Suctorian tentacle, and especially the remarkable tentacule of 

 Asellicola, the fact that all cilia which are large enough to show any 

 structure at all prove to be tubular with an enclosing pellicula, the 



