Marvels of Pond-Life. 29 



gizzard, " it is thrown back by a peculiar scoop-like 

 action of the unci, very curious to witness." The 

 foregoing diagram will help the reader to comprehend 

 this description, but no opportunity should be lost for 

 viewing this remarkable organ busy at work in the 

 living animals. 



The respiration of the Rotifers is supposed to be 

 effected by the passage of water through vessels run- 

 ning round them, and called the " water vascular 

 system," and in addition to their eyes, which often 

 disappear in adult specimens, the organ we described 

 as standing out like a pig-tail, as our acquaintance 

 crawled along, is thought to act as an antenna, or 

 feeler, and brings its possessor in further relation to 

 the external world. It is also called the calcar, or 

 spur, and is furnished with cilia or bristles at its' 

 extremity. 



Sometimes the particles swallowed by the Common 

 Rotifer are large enough for their course to be traced, 

 but there is frequently a great commotion and grinding 

 of the gizzard, without any appreciable cause, although 

 doubtless something is taken in, and when the creature 

 is tired, or has had enough, we see both head and tail 

 retracted, and the body assumes a globular form. In 

 another chapter, when viewing a Philodine, we shall see 

 how in the family to which the Common Rotifer 

 belongs, the gizzard departs from the perfect type. 



