8 



INTRODUCTION TO ZOOLOGY. 



idea receives confirmation from the fact, that by day or night, 

 at whatever period the Polygastrica may be examined, the 

 observer will never find them in a state of repose, or witness 

 them roused to activity by the light. 



The Rotifera present a higher organization than the Poly- 

 gastrica. In them we can trace a nervous system; and we 

 observe muscular bands running over the body, both longi- 

 tudinally and transversely, by means of which they can expand 

 or contract their bodies in any du-ection {Fig. 3). The cilia, 



already mentioned as fringing the lobes 

 on the upper portion of their bodies, 

 by their ceaseless action cause cm-rents 

 in the water, and thus furnish a supply 

 of food, while, at the same time, they 

 act as instruments of progression. 

 The Piotifera feed on the Polygastrica; 

 and they are furnished with an instru- 

 ment by which they can attach them- 

 selves to one spot, and thus, when not 

 inclined to swim about, they can moor 

 themselves at pleasure, and feed at 

 their ease on the nutriment which the 

 currents caused by the action of the 

 cilia bring within their reach. The 

 Eotifera are remarkable for their te- 

 nacity of life. Fontana, an Italian 

 naturalist, kept a number of them for 

 Fig. 3.— Hydatina. two years and a half in dried sand; 

 yet, in two hours after the application of rain water, the 

 greater part recovered life and motion. Spallanzani repeated 

 the experiments with similar results, after having kept the 

 creatures for four years in the torpid state. He further proved 

 their power of revival after apparent death, by alternately 

 drying and moistening the same individuals. He tried this 

 fifteen times; at each exhumation some of the animalcules 

 did not recover — after the sixteenth time, none of them 

 revived. 



The different modes of reproduction among the Infusoria 

 are very remarkable. Some are produced from gems or buds. 

 These appear like little tubercles on the body of the parent — 

 increase in size — assume the form proper to the species — drop 

 off, and become perfect and distinct animals. This mode is 



