E inter on Growth and Inheritance 451 



vorticella with its stalk could only be equivalent to one 

 of the cellular elements whereof the muscular tissue of 

 any multicellular animal is composed. Yet Professor Eimer 

 does not doubt but that the protoplasm in the stalk of a 

 vorticella is really equivalent to the muscular substance of 

 higher animals, and he quotes Klihne 1 to the effect that this 

 particle of vorticella protoplasm ' behaves exactly like frog's 

 muscle, and, even when isolated from the rest of the animal, 

 can be made to contract, and even be tetanised, by the 

 stimulus of variations of an electric current.' But whatever 

 may be the degree of equivalence existing between such 

 practically similar parts, we think the Professor is fully 

 justified in asking,^ ' How could selection, or even sexual 

 mixture, produce muscles at particular parts of the body 

 where previously none were present ? Selection and mixture 

 can only deal with what is in existence.' 



The most important part of the remaining portion of the 

 book treats first of the evolution of the organs of sense, and 

 secondly of the evolution of the whole organism by physical 

 activities which are supposed not to be mysterious. We 

 shall find, however, that these explanations, when even 

 slightly analysed, turn out to be mere words or phrases, 

 which either imply the existence of forces the Professor 

 ignores, or are utterly impotent to suggest any real explana- 

 tion whatever. 



Thus he supposes the ultimate material constituents 

 of the several sense-organs to have been derived from one 

 common layer of cells placed on the external surface of sup- 

 posed primitive and as yet actually insentient organisms. 

 The most external layer came, and comes, first into contact 

 with the outer world. ' All external stimuli acted first upon 

 it. By the repeated incidence of stimuli this layer,' he tells 

 us,^ ' must have become more and more fitted for their recep- 



1 Myologische Untersuchungen. Leipsic. - P. 328. ^ P. 332. 



