58 GENERAL HISTORY OF 



many balls, we likewise remark the circular rotation 

 alluded to, but I cannot, in this instance, say what is the 

 cause of it. 



" Thus, in the true Infusoria, the substances which they 

 absorb are introduced into the abdominal cavity in the 

 form of balls, and from these the stomach extracts the 

 nutritive substances. The residue remains in these same 

 balls, the mucosities interposed are re-absorbed, and even 

 in the interior of the stomach the particles of the ball are 

 disintegrated, although this happens but seldom. 



^' What is the nature of those vesicular cavities, of such 

 great numbers, and so variable in size, which appear in 

 the interior of the Infusoria ? They are not stomachs, 

 they possess nothing in common with the balls of which 

 we have spoken, although the latter may get into them 

 singly, but this can only be considered as accidental. 



" We may trace the formation of these cavities, and 

 perceive their sudden and complete disappearance, with as 

 much ease as the formation of the balls. Nay, more, it 

 .is sometimes possible to see how one of these cavities 

 moulds itself over a ball, and speedily afterwards dis- 

 appears. The microscope shows that these cavities are not 

 lined with a particular membrane, but are mere exca- 

 vations of the pulpy substance. They likewise often 

 appear very near the inner surface of the membrane which 

 forms the skin of the animal, and some of them increase 

 to such a size that their diameter is equal to the third or 

 the half of that of the entire cavity of the Infusoria. 

 The slight refraction which the rays of light undergo at 

 their circumference proves that these cavities are not filled 

 with air, but by a liquid ; and in the large Infusoria, it is 



