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. Whether 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 inJieritance 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- 



