ONE-CELLED ANIMALS 



3 1 



is a breaking up of the nuclei and a part of the micronucleus 

 of each individual passes over to the other. Then the Para- 

 moecia separate and each divides into two. This is, in very 

 simple condition, the process of ferti- 

 lization, which occurs in more elaborate 

 condition in all the higher animals. 



Vorticella. Many other minute or- 

 ganisms will be found in the drops of 

 water that have been examined while 

 looking for the Amoebae and Paramce- 

 cia, but of these we wish to call parti- 

 cular attention to but one. On the 

 leaves or sticks that have been collected 

 from ponds and placed in vessels of 

 water, tiny whitish mould-like tufts 

 may sometimes be seen. Touch such 

 a spot with a needle and it may con- 

 tract instantly. If so, it is probably 

 a colony of Vorticella, or bell animal- 

 cules. Such a mass, examined under 

 the lens, will be seen to be made up of 

 a number of attached slender stalks 

 each having a bell-shaped free end, 

 hence the common name, bell animal- 

 cule. When the stalk is extended it is 

 straight or somewhat curved but when 

 the animal is disturbed the stalk con- 

 tracts into a close spiral. The thick- 

 ened upper outer margin of the bell, 

 the peristome, and the central disk, the 

 epistome, are fringed with rather long 

 cilia. Between the peristome and the 

 epistome is a groove, the mouth or vesti- 

 bule, which leads into the body. The substance comprising 

 the body is differentiated into an outer uniformly granular 

 ectosarc and a more transparent, colorless endosarc, in which 

 are numerous large food vacuoles, a large clear contracting 

 vesicle, a large curved macro-nucleus, and near it a micro- 



F I G . i o . Vorticella 

 sp. One individual with 

 stalk coiled, and one 

 with stalk extended. 

 (From life; greatly mag- 

 nified.) 



