TEE PROTOZOA OF THE SEA SHOSE 



113 



FIG. 63. THREE IXFUSORIANS 

 MAGNIFIED 



cavities that contract at intervals like a heart. Then, in the 

 interior, there is a mass of softer material with cavities tilled with 

 fluid, two solid bodies, and numerous granules. 



In these creatures we find, too, a distinct and permanent mouth, 

 usually funnel-shaped, leading to the soft, interior substance, in 

 which the food material becomes 

 embedded while the process of 

 digestion proceeds. Here, then, for 

 the first time, we meet with a 

 special portion of the body set 

 apart for the performance of the 

 work of a stomach ; and, further, 

 the process of digestion being over, 

 the indigestible matter is ejected 

 through a second permanent open- 

 ing in the exterior cuticle. 



Again, the infusorian does not 

 move by means of temporary 

 pseudopods, as is the case with the lower protozoons, but by means 

 of minute hair-like processes which permanently cover either the 

 whole of the body, or are restricted to certain portions only. These 

 little processes, which are called cilia, move to and fro with such 

 rapidity that they are hardly visible ; and, by means of them the 

 little infusorian is enabled to move about in its watery home with 

 considerable speed. 



In some species a few of the cilia are much larger than the 

 others, and formed of a firmer material. These often serve the 

 purpose of feet, and are also used as a means by which the little 

 animal can anchor itself to solid substances. 



As with the lower protozoons, the infusoria multiply by division ; 

 but, in addition to this, the nucleus may sometimes be seen to 

 divide up into a number of minute egg-like bodies, each of which, 

 when set free, is capable of developing into a new animal. Should 

 the water in which infusorians have been living evaporate to dryness, 

 the little bodies just mentioned become so many dust particles that 

 may be carried away by air currents; but, although dry, they 

 retain their vitality, and develop almost immediately on being 

 carried into a suitable environment. 



Infusorians are so called because they develop rapidly in infu- 

 sions of various vegetable substances ; and those who desire to 

 study their structure and movements with the aid of a microscope 



I 



