i 4 2 INSECTS AND HEREDITY 



Other names have been specially proposed in order to 

 render apparent the distinction between these two classes 

 of characters. Weismann employed terms which set forth 

 their different origin. The inherent characters he called 

 blastogenic, expressing an origin that lay far back in the 

 germ-cell from which the individual arose. Acquired 

 characters he called somatogenic, to express a later origin 

 due to circumstances which had affected the body-cells. 

 The word centrifugal suggests characters developing from 

 within rather than as impressed from without : centripetal 

 conversely suggests characters impressed upon the in- 

 dividual from without, characters which are not the out- 

 come of internal causes. 1 Acquired structural changes 

 have also been spoken of as modifications, the term 

 variation being restricted to characters of germinal origin. 2 

 All the terms suggested for these two classes of cha- 

 racters convey something of a definition. Thus the brief 

 convenient definition of acquired characters as ' those 

 modifications of bodily structure or habit which are im- 

 pressed on the organism in the course of individual life' 3 

 is obviously suggested more or less completely by one 

 set of terms, and ' those characters or properties with 

 which the organism is originally endowed ' 4 by the other 

 set. Another attempted definition of an acquired cha- 

 racter is as follows : — ' Whenever an organism reacts 

 under an external force, that part of the reaction which is 

 directly due to the force is an acquired character.' 6 And 

 although it may be impossible entirely to unravel the one 

 part from the other, certain elements may easily be dis- 

 criminated. For instance, the starting of the reaction as 

 contrasted with the sequence of events which make 

 up the reaction itself is obviously an acquired element, 

 and those who maintain the hereditary transmission of 



1 Theories of Heredity, in the Midland Naturalist, Nov. 1889. Re- 

 printed in the present volume, see p. 120. 



2 Prof. J. Mark Baldwin, A New Factor in Evolution, in the American 

 Naturalist for June and July, 1896. 



s Prof. C. Lloyd Morgan in Baldwin's Dictionary of Philosophy and 

 Psychology, New York, 1901, vol. i, p. 10. 

 * E. S. Goodrich, 1. c, p. 10. 

 5 Nature, vol. li, 1894, p. 55. 



