COMMON PROPERTIES 51 



of the eighteenth century, but it is merely 

 an extreme manifestation of a very primitive 

 property of animal life. My coupling of the 

 cryptozoic habit with the stereotropic reaction 

 is incidentally justified by a statement of Eisig 

 to the effect that stereotropism signifies rest 

 and concealment. The purpose of this and the 

 preceding chapter has been to insist upon the 

 fundamental nature of cryptotaxis and stereo- 

 tropism in the convergent evolution of animals. 

 These are some of the primary properties of 

 living matter upon which the moulding forces 

 of nature have been at work for untold ages. 



A somewhat analogous case, in so far as it is 

 an extreme manifestation of a common property, 

 is the electric power of the three typical kinds 

 of electric fishes (ray, eel of South American 

 rivers, and catfish of African rivers). As shown 

 by E. du Bois-Reymond, 1 these fishes owe their 

 capacity for imparting severe shocks, in different 

 directions, to an intensification of the common 

 electromotive properties of nerve and muscle. 

 In each case, as pointed out by Dr D. S. Jordan, 5 

 closely - related species show no trace of the 

 electric endowment. 



1 See "Biological Memoirs," Oxford, 1887, vol. i. 



2 " Guide to the Study of Fishes," 1905. 



