IX THE HISTORY AND SCOPE. OF ZOOLOGY 377 



occupied themselves with this subject are August 

 Weismann of Freiburg and E. B. Poulton of Oxford. 



It has been argued that the elaborate structural 

 adaptations of the nervous system which are the 

 corporeal correlatives of complicated instincts must 

 have been slowly built up by the transmission to 

 offspring of acquired experience, that is to say, of 

 acquired brain structure. At first sight it appears 

 difficult to understand how the complicated series of 

 actions which are definitely exhibited as so-called 

 " instincts " by a variety of animals can have been due 

 to the selection of congenital variations, or can be 

 otherwise explained than by the transmission of habits 

 acquired by the parent as the result of experience, 

 and continuously elaborated and added to in succes- 

 sive generations. It is, however, to be noted, in the 

 first place, that the imitation of the parent by the 

 young possibly accounts for some part of these com- 

 plicated actions, and, secondly, that there are cases in 

 which curiously elaborate actions are performed by 

 animals as a characteristic of the species, and as sub- 

 serving the general advantage of the race or species, 

 which, nevertheless, can not be explained as resulting 

 from the transmission of acquired experience, and 

 must be supposed to be due to the natural selection of 

 a fortuitously developed habit which, like fortuitous 

 colour or form variation, happens to prove beneficial. 

 Mr. Poulton has insisted upon the habits of " sham- 

 ming dead " and the combined posturing and colour 

 peculiarities of certain caterpillars (Lepidopterous 

 larvae) which cause them to resemble dead twigs or 



