REACTIONS OF DIDINIUM NASUTUM. 



93 



is, it responds with an avoiding reaction similar to that discovered 

 by Jennings in Paramecium, Oxytriclia, etc. One of the striking 



c.-v 



FIG. i. 1 Didinium nasutum, one of the smallest specimens found. Such 

 specimens result when repeated fission takes place in the absence of food. 



FIG. 2. One of the largest not in the process of division. 



FIG. 3. One of the largest specimens just beginning the process of fission 

 as indicated by the additional bands of cilia, c' ; c, primary bands of cilia ; 

 n, nucleus; c.v., contractile vacuole ; s, seizing organ; o.i mm., projected 

 scale. 



FIG. 4. One of the largest monsters seen. The narrow bands of cilia, c', 

 indicate the beginning of fission. 



FIG. 5. A typical specimen selected from a race of exceptionally large 

 Parainecia. Compare with Paramecium in Fig. 6. 



peculiarities about this creature is the fact that in responding with 

 the avoiding reaction, it always turns toward the same side. One 



1 All the figures accompanying this paper were outlined with the camera 

 from specimens killed suddenly with Worcester's fluid and preserved, after 

 washing with water, by adding ten per cent, glycerine solution and allowing it 

 to concentrate by slow evaporation. No change in size or form could be 

 detected during this process. 



