ORGANIC GROWTH 



tractile substance will be least developed, and hence we shall 

 find the most typical connective-tissue-fibres at right angles 

 to the muscle-fibres." l 



When I speak of an effort to contract, I do not of course 

 intend to support Lamarck's view, especially not in the sense 

 that anything can be produced by the " will." 



Contractility is one of the fundamental properties of proto- 

 plasm, and by excessive exercise of this property, according 

 to my explanation, the characteristic muscular substance is 

 produced from the protoplasm. That effort is exerted in this 

 process is self-evident, but this produces an effect not directly, 

 but only indirectly. 



Only thus can be explained the fact that musculature is 

 everywhere most developed in those parts of animals in which 

 its presence is most necessary to their requirements, e.g. in 

 Medusae, which move by the contraction of the bell, on the 

 under side of the bell ; in worms, whose locomotion is due 

 to contortions and creeping and twisting, in the "dermo- 

 muscular tube " ; in snails, in the foot ; in bivalves, in the 

 adductor muscles, etc. 



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. 



But the muscles of multicellular animals afford in yet 

 another direction evidence in support of my view of the 

 modification of organisation by functional activity. 



ORIGIN OF STRIATION IN MUSCLES 



The text -books of histology still continue to divide 

 muscles into the smooth and the transversely striated. On 



1 Vid. Beroe ovatus, 1873, op. cit. p. 30, seq. Similar results have been 

 obtained by my friend Flemming with regard to the connective-tissue- and muscle- 

 cells in the urinary bladder of Salamandra maculata. He says : " There are per- 



