134 SINGLE-CELLED ANIMALS AS ORGANISMS 



Remember that the paramcecium 

 is a semi-fluid body, covered with 

 a membrane. 



Other structures found within 

 the cell are (1) contractile vacuoles 

 (cv), usually one at each end of the 

 cell ; these serve to excrete liquid 

 waste; (2) water vacuoles, clear 

 spaces; (3) the nucleus (n), con- 

 sisting of a double structure, the 

 micro- and the ' macro-nucleus 

 which can be seen only in a 

 stained specimen. (Demonstra- 

 tion.) 



Conclusion. — 1. What struc- 

 tures are found in a one-celled 

 animal ? 



2. What uses have these struc- 

 tures ? 



3. Draw a paramcecium show- 

 ing all structures. 



d. Reproduction 



Observations. — Sometimes 

 paramcecia may be found divid- 

 ing crosswise by fission. In this 

 process each of the two new cells 

 formed contains half the original 

 nucleus and half of the rest of 

 the cell body. Draw such a specimen if you find one. In 

 another method of reproduction, parts of the nuclei of two 

 adjoining cells become exchanged, so that the first cell has part 

 of the nucleus of the second cell and the second cell has part 

 of the nucleus of the first cell. This is known as conjuga- 

 tion. 



Conclusion. — 1. How do paramcecia reproduce? 



2. What is the difference between fission and conjugation? 





A Colonial Type 



