290 M. E, Claparedc on Actinophrys Sol. 



when we get more perfect instruments than those of which we 

 can now avail ourselves. How can we imagine that the will of 

 a nerveless animal can influence a structureless substance ? If 

 we consider how difficult it is to make out the nerves even of 

 comparatively large Radiata, we should not deny the existence 

 of a nervous system because we cannot find it at once. 



As regards Actinophrys Sol in particular, we must either drop 

 the class of unicellular animals altogether, or refer this animal 

 to some other place. Even if we admitted that Actinophrys was 

 the equivalent of a cell, it would still not be unicellular, for an 

 endogenous cell-production has taken place in it. The con- 

 tractile vesicle is nothing but a cell. In other Infusoria it may 

 be considered that this organ is merely a cavity or vacant space 

 in the sarcode. But such an assumption is quite impossible in 

 Actinophrys. In this animal the contractile vesicle is brought 

 to the surface in such a manner, that Siebold, who assumed the 

 existence of an integument, was astonished that this should 

 retain sufficient elasticity to drive the nutritive fluid back into 

 the parenchyma. As it is now certain that Actinophrys possesses 

 no integument, the phsenomenon becomes still more wonderful. 

 The organ, when dilated, looks like a thin soap-bubble, and 

 exhibits a simple margin. How then can we explain the return 

 of the fluid by the contractile sarcode ? Would it not be con- 

 trary to all the laws of mechanics, that the fluid should rather 

 force its way through the tough, thick mass of the body, than 

 break through the extremely thin wall of the contractile vesicle, 

 consisting of the same substance, which alone separates it from 

 the external water ? It is only necessary to observe the action 

 of the contractile vesicle of an Actinophrys for a few minutes, to 

 be convinced of the presence of an including membrane. At 

 least, no doubt remains in our mind upon this point. And if 

 the presence of this membrane in Actinophrys be once received, 

 its existence in the other Infusoria becomes all the more pro- 

 bable. In fact, we are justified in supposing that not only the 

 contractile vesicle, but also the pyriform outlets of Paramecium 

 are clothed with a proper membrane. Kolliker himself sup- 

 poses that the contractile vesicle, when present, is the equivalent 

 of a cell-membrane. With the proof of the existence of such a 

 formation in Actinophrys, his hypothesis of the unicellular con- 

 stitution of that animal consequently falls to the ground. 



.,-,; 



[Throughout this memoir the author speaks of the animal 

 upon which his observations were made as the Actinophrys Eich- 

 hornii of Ehrenberg. In a supplementary note, however, he 

 states that he was in error in the determination of the species, 

 and that the animal was really the A. Sol; under these cir- 



