Marsh Collection, Peabody Museum. 173 



upon which to rest onr "belief in certain factors concerned in evo- 

 lution, we could yet feel reasonably assured that the inherited 

 effects of disuse had played no unimportant part in the retro- 

 gressive changes which these animals have suffered in the past. 



According to the very able researches of Packard and 

 Eigenmann, the loss of sight as well as other important 

 changes in these cave forms can be explained on no other 

 rational hypothesis than that of the inherited effects of disuse ; 

 and while the admission of such explanation, as a fact, may 

 render impossible the construction of a satisfactory theory of 

 heredity, in the light of our present knowledge, then all that 

 can be said is, so much the worse for a theory of heredity.* If, 

 therefore, the inherited effects of disuse are capable of produc- 

 ing such profound modifications as those to which reference 

 has just been made, it follows that the inherited effects of pro- 

 longed use must have been equally potent in the production of 

 change in animal structure. This, I may say, is the kind of 

 evolution that was taught by the great master minds who 

 gave it birth, and, notwithstanding all the subsequent discus- 

 sion which has taken place regarding the factors concerned in 

 the process, I am still firmly of the opinion that the theory of 

 evolution, as set forth by Darwin and Huxley, comes nearer to 

 the truth than all others yet advanced. 



With this understanding of the nature of the causes by 

 means of which we must, in my judgment, seek to explain the 

 progressive changes in brain structure among the Primates, we 

 are now prepared to return to the inquiry. 



It is first necessary to recall that different species of ani- 

 mals seem to employ the special senses in different degrees, for 

 the purpose of acquiring information of any object that may 

 excite their attention. Among such animals as our domestic 

 horse and cow, if confronted by any object new or strange to 

 them, they will at once give evidence of the fact by every 

 attitude of marked attention. If not sufficiently frightened to 

 run away, they proceed to inspect it from every point of van- 

 tage. Sight alone, however, seems to be insufficient to satisfy 

 their curiosity or allay their suspicions, and it is not until they 

 are able to approach near enough to test it fully by the sense 

 of smell that they seem to be able to acquire the necessary 

 information they desire. This same characteristic of depend- 

 ing largely upon the sense of smell is true of many animals in 

 a state of nature. It is quite as much by this means as by the 

 sense of sight that they detect danger. 



As among the hoofed animals, the Carnivora also depend 

 largely upon sight and smell for information. In rare instances, 

 the dog will use his paw for the purpose of turning an object 



*For the evidence in favor of the transmission of acquired characters, see 

 also the works of Hyatt. Kyder, Cope, Beecher, and othei-s. 



