Lecture XXX. 275 



volcanic in origin, and the fact that some of their craters are still 

 active shows that the islands have been formed in comparatively 

 recent geological time. When Darwin first landed on the archi- 

 pelago he was disappointed with the uninteresting appearance of 

 the stunted vegetation. He noticed, however, that this dwarfed 

 vegetation showed an unmistakable relationship with the flora of 

 South America, being composed of the same orders and classes. 

 On further examination he was astonished to find that most of the 

 species were different from those found in South America. Thus 

 of the 175 species of flowering plants found by him in the Gala- 

 pagos, 100 are not known elsewhere in the world, although some 

 of them belong to South American genera. Of the twenty-one 

 species of the order Composite found on the Galapagos twenty are 

 found only there. They belong to twelve different genera, of 

 which ten are peculiar to the archipelago. His examination 

 brought to light another very interesting point. Where a genus 

 was widely spread over the archipelago, the species of that genus 

 found in the different islands differ from one another. Thus a 

 genus of a tree-like composite, Scalesia, which is spread over six of 

 these islands and is found nowhere else in the world, is represented 

 in each island by a different species. Similar instances of this 

 kind of distribution of other genera of plants were found. The 

 analysis of the animal population gave results quite like those of 

 the vegetation, and it is not surprising to learn that it was these 

 observations made on the Galapagos Islands which were directly 

 responsible for turning Darwin's thoughts to the problem of the 

 origin of species. The inevitable conclusion which has to be 

 drawn from these records is that the descendents of most of the 

 colonists since their transit from South America have become so 

 transformed that they no longer belong to the same species as their 

 relatives remaining in South America. In the case of the genus 

 Scalesia and many others this transformation has been so profound 

 that the descendants of the colonists and those of their stay-at- 

 home relatives can no longer be classed as belonging to the same 

 genus. The occurrence of different species on the six different 

 islands affords conclusive evidence that new species have arisen in 

 the archipelago, and that the observations cannot be explained by 

 the dying out of the parent stock on the adjacent continent. The 

 large number of species peculiar to the islands, and the fact that 

 these species belong to the most various classes and orders, also 

 preclude this view. The smaller number of species common to the 

 islands and the adjacent continent may be attributed to the stability 

 of these species, but with greater probability to their more rocent 



