38 GENERAL HISTORY OF 



Pohjgastric. If solid substances do not exist in the siiironnding 

 liquid, then the balls are less solid, and they appear in the forms 

 which they present in the Infusoria plunged in colourless liquids. 

 In this case, the balls are composed of a small number of particles, 

 and princi])ally of a considerable mucous mass, which ujiites them. 

 Sometimes two balls of this kind are so pressed against each other 

 by the contractions of the animal, that they at last unite. 



" If you wish to follow the formation of these balls, it is necessary 

 to commence these observations at the moment when the Infusoria 

 are plunged into the coloured liquid. The deglutition of the 

 coloui-ed particles takes place very quickly, often in about half a 

 minute, and the coloured balls issue one after another from the 

 stomach, and are pushed downwards along the internal wall of the 

 cavity of the animal. In the genera Paramecium, Kerona, and Vor- 

 ticella, the new ball pushes the preceding before it, along with the 

 mucosities between them, in such a manner that the fii'st rises along 

 the opposite wall, rotiu-ns to the other extremity of the ca'ST.ty, and is 

 jjushed downwards on the other side. The balls thus accumulate in 

 succession, till they are expelled, one after the other, by the anus. 

 The number of these balls is often so considerable, as to fill the 

 whole cavity of the animals, and so close together, that they form a 

 large mass, which turns slowly xq^on itself, as among the Vorticelh. 



" This rotation is the result of the force with which the newly- 

 formed ball is pushed from the stomach into the cavity, and moves 

 along the under side of the preceding ball. In other cases, where 

 there are not yet many balls, we likewise remark the cii'cular rota- 

 tion 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 caAdty 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 anterior of the stomach the particles of 

 the baU are disintegrated, although this happens but seldom, 



" What is the nature of those vesicular cavities, of such gi-eat 

 numbers, and so variable in size, which appear in the interior of tho 

 Infusoria ? They are not stomachs, they possess nothing in conimon 



