14 PRESIDENT'S ADDRESS. 



fertilization, and thereby maintaining a vigorous and prolific 

 vegetation. 



The seasonal changes of colour to which the coats and furs of 

 animals are subject, especially in Polar regions, seem to be due to 

 the action of light and heat upon the pigmefnt-cells and upon the 

 chlorophyll-cells in the case of plants. With regard to instinct, 

 much intelligence is apparent amongst the lowest and most rudi- 

 mentary forms of animal life, which could not have been evolved 

 but are original and primary. The questions, both of coloration 

 and of instinct, are highly interesting. Are protective or attractive 

 coloration and instinct exclusively the product of natural selection 

 or the results of an overruling, directing, intelligent mind ? 



Among the various problems connected with Darwinism, none has 

 engaged more attention than that of heredity, the more so just now 

 owing to the publication of Doctor Weissman's tracts on the subject, 

 which have recently become accessible to the general reader by an 

 English translation from the German. To explain the process which 

 persistently carries organisms through successive generations, uniting 

 the ancestor with its most recent descendant, has engaged the 

 attention of biologists since the time of Hippocrates. There is a 

 recognised tendency of every organism to produce its like, or 

 varying from it slightly, and in every case the parent transmits to 

 the offspring structural modifications and functional peculiarities. 

 A constant struggle for existence follows these changes ; the 

 swiftest, strongest, hardiest, and colour favouring concealment in the 

 case of animals ; strength of shoot, period of flowers or seeding, 

 armature, colour, or odour to attract insects in the case of plants. 

 In the case of unicellular organisms, which multiply by fission, and 

 when the two parts are exactly alike in size and structure, 

 heredity depends simply upon the continuity of the individual 

 during the uninterrupted process of fission ; but in the case of 

 multicellular organisms, which do not increase in numbers by simple 

 division, but multiply by means of sexual reproduction, great 

 difficulties arise to account for the principle of heredity. Darwin's 

 theory of Fangenesis, which he put forward as a provisional 



