26 POPULAR ILLUSTRATIONS OF 



CHAPTER II. 



THE INFUSORIA (continued}. 



IN the early period of our acquaintance with the infusorial aninial- 

 culae a very erroneous idea of their structure was entertained by 

 naturalists. This was principally owing to the fact that Ehrenberg, 

 to whose investigations our knowledge of the vast number of species 

 was principally due, was not so good a comparative anatomist as he 

 was an observer. Hence the lowly infusorial animalculae were placed 

 in a much higher position in the animal kingdom than they can lay 

 claim to. Muscular power, nerves, a blood circulation, and a multi- 

 plicity of stomachs (hence their name Polygastricci) were assigned 

 to them, without any foundation in fact. They are unicellular 

 Protozoons. Before I make this obvious, let me say a word or two 

 about one or two parts of their organisation which they have in 

 common, and which will be frequently alluded to. 



Sarcode is the term which has been assigned to the jelly-like sub- 

 stance of which the bodies of the Protozoa are formed. It has been 

 called liquid flesh. It is, however, the substance which supplies the 

 place of flesh in the lowest animals, and resembles it in chemical 

 composition, but differs in the absence of muscular fibre. It is 

 semi-transparent and variable in colour. It is insoluble in water ; 

 and, when dried, its physical characters are restored by immersion. 

 Its singular properties will be noticed as we proceed in the descrip- 

 tion of the Protozoa. All the bodies of the Protozoa, including the 

 Gregarinae, are formed of this substance. 



Cilia are the minute hair-like bodies which fringe the oral aper- 

 tures, and in some instances all the surfaces, of the Protozoa. They 

 occur in both vegetable and animal structures, from the Volvox 

 globator up to man himself. They have very remarkable properties, 

 either as organs of locomotion, or as, by their rapid motion, the 

 cause of currents by which food is drawn into the mouths of 

 creatures otherwise unable to obtain it. On a large and familiar 

 scale, they are illustrated by the human eye-lashes. They are from 

 02 to '00005 of an inch in length in the Protozoa, and their move- 

 ment is so rapid, that they are frequently invisible through the 

 microscope, anid their presence only inferred by the currents which 

 they produce. They move uniformly with regard to each other, each 

 bending from its base to its point at the same instant of time. This 

 motion ceases or commences in obedience to what appears to be the 

 will of the lump of jelly constituting the Protozoon. 



Let us now take one of the best known forms of the Infusoria, 

 Paramcecium Bursaria, and with the aid of the cuts we shall be able 



