376 THE HISTOKY AXD SCOPE OF ZOOLOGY IX 



advanced as only to be explained on the Lamarckian 

 assumption are found on examination and experiment 

 to be better explained, or only to be explained, by the 

 Darwinian principle. Thus the occurrence of blind 

 animals in caves and in the deep sea was a fact which 

 Darwin himself regarded as best explained by the 

 atrophy of the organ of vision in successive genera- 

 tions through the absence of light and consequent 

 disuse, and the transmission (as Lamarck w^ould have 

 supposed) of a more and more weakened and structu- 

 rally impaired eye to the offspring in successive 

 generations, until the eye finally disappeared. But 

 this instance can, I think, be fully explained by the 

 theory of natural selection acting on congenital for- 

 tuitous variations. Many animals are thus born with 

 distorted or defective eyes whose parents have not 

 had their eyes submitted to any peculiar conditions. 

 Supposing a number of some species of Arthropod or 

 Fish to be swept into a cavern or to l^e carried from 

 less to greater depths in the sea, — those individuals 

 with perfect eyes w^ould follow the glimmer of light 

 and eventually escape to the outer air or the shallower 

 depths, leaving behind those with imperfect eyes to 

 breed in the dark place. A natural selection would 

 thus be effected. In every succeeding generation this 

 would be the case, and even those with weak but still 

 seeing eyes would in the course of time escape, until 

 only a pure race of eyeless or blind animals would be 

 left in the cavern or deep sea. Experiments and 

 inquiries with regard to transmission of acquired 

 characters are in progress ; amongst those who have 



