I A CHAPTER IN DARWINISM 41 



power of feeding on the carbonic acid dissolved in the 

 water around them just as green plants do. This 

 would lead to a degeneration ; they would cease to 

 hunt their food, and would bask in the sunlight, taking 

 food in by the whole surface, as plants do by their 

 leaves. Certain small flat worms, by name Convoluta, 

 of a bright green colour, appear to be in this condition. 

 Their green colour is known to be the same substance 

 as leaf-green ; and Mr. Patrick Geddes has recently 

 shown that by the aid of this green substance they 

 feed on carbonic acid, making starch from it as plants 

 do. As a consequence we find that their stomachs 

 and intestines as well as their locomotive organs be- 

 come simplified, since they are but little wanted. 

 These vegetating animals, as Mr. Geddes calls them, 

 are the exact complement of the carnivorous plants, 

 and show how a degeneration of animal forms may be 

 caused by vegetative nutrition. 



Another possible cause of degeneration appears to 

 be the indirect one of minute size. It cannot be 

 doubted that natural selection has frequently acted on 

 a race of animals so as to reduce the size of the indi- 

 viduals. The smallness of size has been favourable to 

 their survival in the struggle for existence, and in 

 some cases they have been reduced to even microscopic 

 proportions. But this reduction of size has, when 

 carried to an extreme, resulted in the loss or sup- 

 pression of some of the most important organs of the 

 body. The needs of a very minute creature are limited 

 as compared with those of a large one, and thus we 

 may find heart and blood-vessels, gills and kidneys, 



