THE TREE VORTICELLA. 49 



stem in the same manner as tlie former species, tra- 

 verses the water in freedom for awhile, and then be- 

 comes fixed, and goes through the allotted phases of its 

 existence. 



In another kind of Carchesiunii the stem is also spi- 

 rally contractile, and branched by imperfect self-division, 

 and the clusters appear like miniature trees or shrubs. 



LiGN. 3.— The Carchesium, or Tree Vorticelxa. 

 a. The Group expanded. b. The whole Group contracted into a globular mass. 



One of these groups is here represented, as seen with a 

 low power; it is shewn extended in fig. a, and contracted 

 into a ball, in fig. b. 



Physiological Summary. — In this rapid survey of 

 the Polygastria contained in the drops of water under 

 review, the principal chai'acters of this class of animal- 



£ 



