42 



THE MICROSCOPE AND ITS REVELATIONS. 



stroke is made too quickly to be seen ; and the real direction of the 

 movement is then opposite to the apparent. In this back-stroke, when 

 made slowly enough, a sort of ' feathering ' action may be observed ; the 

 thin edge being made to cleave the liquid, which has been struck by the 

 broad surface in the opposite direction. It is only when the rate of 

 movement has considerably slackened, that the shape and size of the 

 cilia, and the manner in which their stroke is made, can be clearly seen. 

 Their action has been observed to continue for many hours, or even days, 

 after the death of the body at large. As cilia are not confined to Ani- 

 malcules and Zoophytes, but give motion to the zoospores of many Proto- 

 phytes ( 248), and also clothe the free internal surfaces of the respiratory 

 and other passages in all the higher Animals, including Man (our own 

 experience thus assuring us that their action takes place, not only with- 

 out any exercise of will, but even without consciousness), it is clear that 



FIG. 304. 



FIG. 305. 



A, Kerona silurus : a, contractile vesicle ; 6, mouth ; Group of Vorticella nebuliferu show- 

 er, c, Animalcules swallowed by the Kerona, after hav- ing A, the ordinary form ; B, the same 

 ing themselves ingested particles of indigo. B, Parame- with the stalk contracted ; c, the same 

 cium caudatum : a, a, contractile vesicles ; b, mouth, with the bell closed ; D, E, F, successive 



stages of fissiparous multiplication. 



to regard Animalcules as possessing a ' voluntary ' control over the action 

 of their Cilia, is altogether unscientific. 



436. In the Ciliated Infusoria, the differentiation of the sarcodic sub- 

 stance into 'ectosarc' or cell-wall, and 'endosarc' or cell-contents, 

 becomes very complete ; the ectosarc possessing a membranous firmness 

 which prevents it from readily yielding to pressure, and having a definite 

 internal limit, instead of graduating insensibly (as in Khizopods) into 

 the protoplasmic layer which lines it. A ' nucleus ' seems always present; 

 being sometimes f parietal ' (or adherent to the interior of the ectosarc), 

 in other cases lying in the midst of the endosarc. In many Ciliata a 

 distinct ' cuticle ' or exudation-layer may be recognized on the surface 

 of the ectosarc ; and this cuticle, which is studded with regularly 

 arranged markings like those of Diatomacese, seems to be the representa- 

 tive of the carapace of Arcella, etc. (Fig. 291), as of the cellulose coat of 



