2<S8 EVOLUTION AND MANKIND. 



and useful experimental observations can be made on a small 

 scale in a zoological laboratory during breeding experiments. The 

 evidences for evolution may be set forth under a number of 

 separate categories, briefly described as classificatory, morpho- 

 logical, enxbryological, distributio.nal or regiional amd paJaeo- 

 zoological, which, combined, give the evidence of the past and 

 present, and enable a forecast to be made as to the forms of the 

 future. These evidences may now be briefly considered. 



Classification is the organised arrangement of animals 

 based on common characteristics. Every attempt to classify 

 animals results in an arrangement which to some extent suggests 

 the evolution of its members. There are said to be about a 

 million different species of living animals in the world, nearly 

 half of which are stated to belong to the Insecta. Modification 

 in different directions of groups of members of a single species 

 results in the production of new species, which, in the course 

 of time, become more and more unlike the ancestral stock, until 

 they themselves attain generic rank. Species, genera, families, 

 orders, classes, phyla are like the twigs and branches of a genea- 

 logical tree, and the sub-divisions of any group have arisen by 

 descent with modification along definite directions. Again, 

 between one group and a neighbouring, divergent group, annec- 

 tant forms have been discovered, such as Peripatus, well known 

 in South Africa, which animal forms a link between the Annelida, 

 or segmented worms, and the Arthropoda, such as Myriapods, 

 Insects and Crustacea. Indeed, all known kinds of animals have 

 been arranged or classified in the form of a comprehensive genea- 

 logical tree, perhaps not quite accurately, for it is likely that 

 several such trees or parts of trees would be needed adequately 

 to express the correct relationships 



The evidences of evolution froaii the point of view of 

 Morphology or Structure are abundant. Considering various 

 types of the vertebrate world, it is easily seen that there is a 

 common plan underlying the organisation of each of the sub- 

 divisions of that group. While there is a general uniformity of 

 the main plan, there are definite modifications that characterize 

 the various sub-divisions. Thus, while the fore-limb of a frog 

 and of a lizard, the wing of a bird, the fore-limb of a rabbit, the 

 paddles of a whale, and the hand of a man are all built on the 

 same plan, the parts are of different shapes and relative sizes 

 in the several cases. Organs which are believed to have origin- 

 ated by modification of the identical organ Of an ancestral animal 

 are said to be homologous. The wings of a bat and of a bird are 

 homologous alike with the arms of a man, the paddles of a whale 

 and the fore-foot of a horse, and contain the same essential bony 

 structures. Analogous organs are those having the same function 

 or use, but a different origin, examples being the wings of a 

 bird and of an insect. The successive adaptations seen in homo- 

 logous organs of a series, of forms also afford strong evidence 

 of evolution. 



Nature does not fully obliterate morphological records of 



