Evidence from Protozoans 369 



such a force? 



He wlio persistently denies that a sensible object is ex- 

 planatory in a causal sense of the forces and activities it 

 manifests because he cannot see the whole rationale of the 

 manifestations, but insists that the final explanation must 

 lie deeper, is at heart an apostate to obsei'vational science, 

 and it matters not at all so far as principle is concerned, 

 whether the invisible "deeper" cause, supposed to be final, 

 be conceived as pure Matter, pure Energy, pure Spirit, 

 or a Divinity. 



To recapitulate: the only conclusive proof of what bodies, 

 whether chromosomes, mitochondria or any other substances, 

 are "bearers of heredity," is either direct or indirect ob- 

 servation that these bodies or substances transform into 

 organic parts which after transformation are seen to re- 

 semble the corresponding parts of the organism's parents. 

 And only such hypotheses concerning the nature of germ- 

 cells as are made in strict accordance with the rule of evi- 

 dence thus fomiulated, are legitimate hypotheses. 



So far as fundamental principles are concerned, we might 

 consequently go no further with the examination of details. 

 However, since the principles are in reality only the general- 

 ized details, and the details are the mother liquor, so to say, 

 of the science of heredity, we can hardly avoid pushing our 

 examination somewhat farther. We will look at a few more 

 examples among the protozoa where cytoplasm and various 

 substances other than chromatin are a physical basis of 

 heredity, these examples being chosen to connect with our 

 studies of the anatomy and development of protozoans in a 

 former chapter. It will be recalled that from the great 

 and highly developed class of Ciliata to which Stentor be- 

 longs we examined Diplodinium and Stylonychia, shown in 

 figures 1 and 3. 



