96 Life and Death, Heredity and Evolution 



largely validates this large mass of material; it shows that 

 hereditary changes of the kind which appear to occur in 

 much bacteriological work, actually do take place when 

 the matter is studied with all the required precautions. 

 Summaries of much of this work, with references to the orig- 

 inal papers, will be found in the publications of Dobell 

 (1912), Jollos (1914) and Pringsheim (1910). 



#. Modifications of Inherited Characters in Higher 



Protozoa 



A relatively small amount of work has of late been done 

 on the modification of inherited characters in the larger and 

 more complex forms of Protozoa; some of the results here 

 perhaps throw light on the nature of the processes occur- 

 ring. 



In the parasitic flagellates Trypanosoma, facts similar to 

 some of those above described for bacteria have been dem- 

 onstrated. A good review of the facts has been given by 

 Dobell (1912). One case introduces a new element, which 

 possibly throws light on certain general relations. The 

 trypanosome possesses, besides a typical nucleus, a small 

 body known as the kinetonucleus (see Figure 27, 2). This 

 structure is placed close to the inner end of the motile 

 flagellum, and may have some relation to the activity of 

 the latter. In reproduction, the kinetonuclei of the two 

 progeny are formed by division of the kinetonucleus of the 

 parent. In Trypanosoma brucei cultivated in mice, it was 

 found that when certain chemicals were injected into the 

 mice, the kinetonucleus of the trypanosomes disappears 

 (Figure 27, 1). The animals now multiply as usual, but 

 remain without kinetonuclei; this continues indefinitely. 

 Thus by the action of the chemicals a stock has been ob- 

 tained which differs structurally from the original race; 



