ACQUIRED CHARACTERS 41 



This result leaves no doubt that light is a necessary stimu- 

 lus for full development of the eye in Proteus, and it is the 

 absence of this stimulus which has led in part to the present 

 degenerate condition of the eye. \^^lether or not the degen- 

 eration has advanced from generation to generation is of 

 course conjectural, but seems highly probable. Weismann 

 indeed considered the evidence for the progressive degenera- 

 tion of disused organs so strong that he framed a special 

 hypothesis, that of germinal selection, to account for it. To 

 this matter we shall return later. 



9. Instincts. Instincts are among the most vital posses- 

 sions of animals, but the same difference of opinion exists as 

 regards their origin as concerning the origin of other adap- 

 tive characteristics of organisms. Without being taught, 

 animals do generation after generation the same acts in the 

 same way. They seem to know, without individual experi- 

 ence or education, exactly what to eat, and how to secure it; 

 how to prepare a nest or burrow of a very definite pattern; 

 how to care for young, though they have never seen young 

 cared for before; what to do as the seasons change; and 

 numberless other vital and necessary things. Some say this 

 is inherited memory, nothing less; the ancestors have learned, 

 their descendants remember. Just as brain cells, after re- 

 ceiving a variety of sensations one after another, are able to 

 reproduce them again in the same order and complexity 

 through memory, so the reproductive cells become store- 

 houses of racial experience or habit which they transmit as 

 instincts. This easy way of accounting for instincts as habits 

 registered like phonograph records in the germ-plasm has 

 even been extended to all inheritance by a number of writers, 

 represented at the present time by Richard Semon. This 

 idea had great influence in America in the last quarter of the 

 last century, when a strong school of modern Lamarckians, 

 or neo-Lamarckians, flourished here. Many still hold to 

 this view, but the neo-Darwinians, or followers of Weismann, 

 have of late been rather in the ascendancy. In their view, 

 instincts arise because the structure of the germ-plasm neces- 



