12 HANDBOOK OF INVERTEBRATE ZOOLOGY. 



IX. The nucleus and nucleolus. In some species there 

 is one nucleus or endoplast at each end of the body, and in 

 others only one near the middle. They are club-shaped 

 masses (Fig. 2, h) of granular protoplasm of a firmer con- 

 sistency than the suri'ounding endosarc. They are some- 

 what difiicult to see in the living animal, but they may be 

 made more conspicuous by adding a little acetic acid to 

 the water. Close to the nucleus is a much smaller body, 

 the nucleolus. 



X. Make a sketch showing as many of these points as 

 possible. 



III. THE STRUCTURE OF VORTICELLA. 



Any of the numerous species of Peritrichous Infusoria 

 may be used to verify the following description, since the 

 difierences between them are very slight. The Vorticel- 

 lidse are abundant in both fresh and salt w^ater ; and many 

 specimens will probably be found in the hay infusion, 

 which has been employed to propagate Paramoecia. 

 Good specimens for examination may nearly always be 

 obtained from a small aquarium, which has been well 

 stocked with water-plants and kept for a few wrecks in a 

 well-lighted place. A glass gallon-jar makes a very con- 

 venient aquarium for this purpose, and it should contain 

 no fishes, newts, or other animals large enough to devour 

 the vorticellas. 



Although the individuals are microscopic, they are 

 frequently found, in such an aquarium, in colonies of 

 a suflScient size to be recognized by the eye without 

 difiiculty. 



If the leaves and stems of the water-plants are care- 

 fully examined, under ivater, either with or Avithout a 



