INFUSORIA. 47 



cn passing through the gullet are directly received into the 

 central mass of diffluent sarcode, where they undergo a kind of 

 slow circulation or rotation. As in the case of the Amoeba, 

 each particle of food generally carries with it a little water, so 

 that the appearance is produced of a number of little clear 

 spaces in the central sarcode. These are now called vacuoles, 

 or food-vacuoles ; but they were originally described by Ehren- 

 berg, the famous Prussian microscopist, as so many distinct 

 stomachs, in consequence of which he named the Infusoria the 

 Polygastrica (Gr. polus, many; and gaster, stomach). The 

 vibrating cilia which clothe the surface of Paramoecium serve 

 partly to drive the animal rapidly through the water, and partly 

 to set up currents by means of which food is conveyed to the 

 mouth. All the nutrient particles obtained in this way undergo 

 the circulation in the central garcode above spoken of, where 

 they are partially or completely digested. The indigestible 

 portions of the food appear to be got rid of by a second aper- 

 ture (anus) placed near the mouth. The only other organs 

 possessed by Paramoecium are the so-called nucleus and 

 nucleolus, and the contractile vesicle (or vesicles), all of which 

 appear to be situated in the cortical layer of the body. The 

 nucleus (Fig. 10, n) is a little solid body, composed of an ex- 

 ternal membrane, with granular contents, and having the 

 nucleolus («') firmly attached to its exterior in the form of a 

 little spherical particle. Both appear to be organs of repro- 

 duction, the nucleus being an ovary, and the nucleolus a 

 spermarium. The names, therefore, of nucleus and nucleolus 

 are extremely inappropriate, as they lead to confusion with the 

 wholly distinct structures which receive these names in an 

 ordinary animal or vegetable cell. The contractile vesicle («) has 

 exactly the same structure as in the Amoeba. It is simply a 

 little contractile cavity filled with a fluid apparently derived 

 from the digestion, and contracting and dilating at regular 

 intervals. There is usually only a single vesicle present, but 

 there may be two or more. 



Reproduction in Paramoecium may be effected by fission — 

 that is to say, by a simple splitting of the body of a single in- 

 dividual into two portions, each of which becomes a fresh 

 being. The process of fission may commence at the surface, 

 or it may begin at the nucleus. In other cases, two Para- 

 m.oecia come together and adhere closely to one another. The 

 nucleus and nucleolus enlarge, and the nucleolus of each is 

 transferred to the other, apparently through the mouth. As 

 the result of this, numerous germs are produced, which, after 



