1 84 THE METHOD OF DARWIN. 



problem of the relation between muscle and 

 the electric organs. With the explanation, it 

 furnishes a good example of how investigation 

 dissolves difficulties. 



It is a common saying that the solution of 

 one problem leads to new and frequently more 

 difficult ones. It may almost be said an inves- 

 tigation should be viewed with suspicion if it 

 does not leave more new problems than it started 

 out to solve. The belief of Fritsch that the 

 electric organs of Malapterurus are homologous 

 with the cutaneous glands opened up a new 

 phase of the general problem of the origin of 

 electric organs. Another difficulty presented 

 itself to Fritsch in the process of solving the 

 original problem which he set before himself. 

 In his study of the innervation of the electric 

 organs of Mormyrus he found that the nerves 

 which supply the electric organs decussate, or 

 cross from one side of the body to the other, 

 after leaving the spinal cord as anterior roots, 

 much as the optic nerves form the optic 

 chiasma within the brain-case. There is no 

 similar case known of nerve fibres crossing 

 from one side of the body to the other after 

 they have left the central nervous system ; and 

 Fritsch properly thinks it to be more difficult 

 to explain by gradual variation and natural 



