xxxiv- Proceedings. 



the.seriea of living forms, Jiowever, was not with a continuous 

 chain, but rather with a tree, the branches from the trunk not 

 all tending upwards, but some sideways, and some even down- 

 wards, so as to fill every space in nature with some appropriate 

 inhabitant. He considered the theory of evolution under the 

 following aspects: — 1. The history of the idea in the human 

 mind. 2. The evidence for evolution afforded by morphology. 

 3. The evidence afforded by embryology. 4. The evidence 

 afforded by palteontology. 



1. — The idea of evolution seems to have been first mooted by 

 the Greek philosopher Anaximander (b.c. 611), who held that all 

 land animals had been primarily marine. Owing, however, to the 

 omission to verify their ideas by an appeal to observation and 

 experiment, Greek speculators often went very far wrong. Bruno, 

 in medieval times, also mooted similar ideas, but the general 

 tendency of the thought of the age was hostile, and no advance 

 was made until the present century. Lamarck (1809) held that 

 the slowly changing external conditions under which living 

 forms were placed would necessitate use and disuse of par- 

 ticular organs, and that this use or disuse produced changes 

 of structure, which were handed down to the descendants. 

 Agassiz pointed out that in descending from the higher to the 

 lower forms of life the structure became simpler and simpler, and 

 that a similar progress was met with as we went back in the 

 history of development of the individual, and in geological his- 

 tory. The successive introduction of higher forms of life did 

 not however entirely supplant the lower forms, but compelled 

 them to take a subordinate place. This author, however, held 

 that new forms of life appeared as the result of special creation, 

 and not by development from pre-existing forms. Darwin, on 

 the other hand, believed that the numerous different forms of life 

 arose from one or a few original forms. He pointed out that the 

 principle which Malthus had enunciated for the human species, 

 viz., that the multiplication of individuals tended to take place 

 at a greater rate than the means of subsistence for them, appUed 

 to all living beings ; hence there was a perpetual struggle for 

 existence, in which those varieties which adapted themselves to 

 changing conditions survived, while others did not. Weismann, 

 while accepting the theory of descent, denies the transmission of 

 acquired characters. He holds that the " body cells," which 

 minister to the nutrition of the individual, are fundamentally 

 distinct from the " germ cells," which perpetuate the race ; and 

 that acquired characters affect only the body cells, and not the 

 germ cells ; while the latter alone transmit characters. It has 

 yet however to be proved that the body cells do not act on the 

 germ cells, and the controversy is still progressing. 



2. — Evidence in favour of evolution is afforded by morphology 



