62 The Unity of the Organism 



cells. But such repetition would be useless for the present dis- 

 cussion. Striated muscle tissue is specially favorable for testing 

 hypotheses about inheritance material from the functional side 

 as well as from the structural s.ide. For example, there are innu- 

 merable differences, larger and smaller, in the limb movements 

 of animals belonging to different species and genera. I know of 

 no observations which precisely connect activities of this sort 

 with muscle tissue; but information concerning the electromotor 

 force in various animals is available. The following on the au- 

 thority of Englemann, taken from Winterstein will serve our 

 purpose. The values are those of the "demarcation current" of 

 galvanic electricity of heart muscle, this current being generated 

 by making a cut surface at the base of the heart and the natural 

 surface at the apex act as a galvanic pile: 25 



Animal species Electromotor force in D. 



Anguilla fluviatilis 0.0265 



Rana esculenta 0.031 1 



Triton cristatus 0.0124 



Tropidonotus natrix 0.036 



Testudo graeca 0.022 



Columba livia 0.0458 



Cygnus oler 0.0168 



Mus musculus v. albino 0.040 



Mus rattus v. albino 0.0446 



Lepus cuniculus 0.0363 



These investigations appear to have been made from the stand- 

 point of general physiology, and therefore not to have been car- 

 ried out with the systematic exactness and exhaustiveness de- 

 manded for taxonomic discrimination. We may consequently 

 presume that more searching examination of the same series 

 would considerably modify these results, but we have no reason 

 to suppose that they would eliminate altogether the differences 

 due to the animal species^ 



After due allowance is made for the purely physiological 

 and environic causes which undoubtedly explain a great 

 many of these differences, probably no biologist would hesi- 

 tate to grant that many of them have an hereditary basis. 

 Turning again to the question of the seat of the hereditary 



