Evidence from Protozoan.'} 3(50 



such a force? 



Pie who persistently denies tliat a sensil)le object is ex- 

 planatory in a causal sense of the forces and activities it 

 manifests because lie caiuiot see the whole rationale of the 

 manifestations, but insists that the final exphuiat ion must 

 lie deeper, is at heart an apostate to oljservational science, 

 and it matters not at all so far as ])ri!icij)le is concerned, 

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

 be conceived as jmre Matter, pure Energy, i)ure Sj)irit, 

 or a Divinity. 



To recapitulate: the only conclusive j)roof of what Ixxlies, 

 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 ])arts of the organism's ]iarents. 

 And onl}^ such hypotheses concerning the nature of germ- 

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

 dence thus fornudated, are legitimate hypotheses. 



So far as fundamental princi})les are concerned, we might 

 consequently go no further with the examination of ditails. 

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

 ized details, and the details are the mother liijuor, 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 ])hysical basis of 

 heredity, these examples being chosen to coiuiect with our 

 studies of the anatomy and devel()]mient of ])rotozoans in a 

 former chapter. It will be recalled that from the great 

 and highly developed class of Ciliata to which Strntor l)e- 

 longs we examined Diplodiniuni and Stt/Ionijchia, shown in 

 figures 1 and 3, 



