22 Evolution and Adaptation 



Organs of Little Use to the Individual 



In every organism there are parts of the body whose 

 presence cannot be of vital importance to the individual. 

 We may leave out of consideration the reproductive organs, 

 since their presence, as has just been stated, is connected 

 with the continuation of the race. The rudimentary organs, 

 so-called, furnish many examples of structures whose pres- 

 ence may be of little or of no use to the individual ; in fact, 

 as in the case of the appendix in man, the organs may be a 

 source of great clanger to the individual. In this respect the 

 organism is a structure not perfectly adapted to its conditions 

 of life, since it contains within itself parts that are of little 

 or of no use, which may even lead to its destruction, and may 

 often expose it to unnecessary danger. Nevertheless such 

 parts are surprisingly infrequent, and their presence is usu- 

 ally accounted for on the supposition that in the past these 

 organs have been of use, and have only secondarily come to 

 play an insignificant part in the functions of the organism. 

 Another example of the same thing is found in the rudi- 

 mentary eyes of animals living in the dark, such as the mole 

 and several cave animals, fishes, amphibia, and insects. 



There are still other organs, which cannot be looked upon 

 as rudimentary, yet whose presence can scarcely be consid- 

 ered as essential to the life of the individual. It is with this 

 class that we are here chiefly concerned. For instance, the 

 electric organs in some of the rays and fish can hardly 

 protect the animal from enemies, even when as highly devel- 

 oped as in the torpedo ; and we do not know of any other 

 essential service that they can perform. Whether the same 

 may be also said of the phosphorescent organs of many 

 animals is perhaps open in some cases to doubt, but there 

 can be little question that the light produced by most of the 

 small marine organisms, such as noctiluca, jellyfish, cteno- 

 phores, copepods, pyrosoma, etc., cannot be of use to these 



