46 



BIOLOGY 



ment. This has been made even more evident and brought to 

 a point beyond discussion by a study of the functions of the 

 nucleus. 



A nucleus is necessary to the complete life of a cell. Among 

 the unicellular animals are some cells large enough for experi- 

 menters to cut to pieces in order to study the different functions 

 of the fragments. These experiments are very difficult and deli- 

 cate, but they have been carried on by a number of investigators 

 independently, who have demonstrated the following facts: If 

 a cell is cut to pieces in such a way that each piece contains a 

 fragment of the nucleus, each fragment is capable of carrying 

 on independently all life functions. Each can feed, grow, and 



FIG. 16. STENTOR. 

 A SINGLE-CELLED 

 ANIMAL; M , THE 



LONG NUCLEUS 



FIG. 17. SHOWING HOW THE STENTOR, 

 WHEN CUT INTO TWO PIECES ALONG 

 THE LINE AB, DEVELOPS INTO TWO 

 COMPLETE ANIMALS 



multiply, and seems to be lacking in none of the essential func- 

 tions of life; Figs. 16 and 17. If, however, the animal is cut to 

 pieces in such a way that some of the fragments contain 

 pieces of the nucleus, while others contain none, the frag- 



