62 LECTURES ON BIOLOGY 



so radical that the existence of any relationship seems excluded. 

 But the boundary becomes less distinct when we come to simpler 

 forms. Let us, for instance, examine the coral-stock with its 

 tree-like branches, its many hundreds of individual inhabitants 

 and, simultaneously, builders the polyps which peep like tiny 

 blossoms from the branches of this tree ; or the closely related 

 sea-anemone, large numbers of which clothe the rocks at the 

 bottom of the Southern seas as with a brilliant flower-carpet. 

 Here even a trained observer might often be doubting whether 

 he is looking at an animal or a plant. As recently as the end 

 of the seventeenth century even naturalists counted both corals 

 and sea-anemones among plants. When the French physician 

 and zoologist, Peysonnel, endeavoured to prove the animal 

 nature of these organisms, and submitted his discovery to the 

 Academy of Sciences in Paris, the President of the Academy, the 

 famous physicist Reaumur felt it his duty to suppress the 

 name of the author of such an improbable assertion. And yet 

 the organization of the polyps shows that they are undoubtedly 

 animals. 



Everyone knows the skeleton of the bath-sponge. Who 

 would think that sponges are animals ? Firmly fixed to the 

 bottom of the sea, the sponge is betraying with not a single 

 motion that it is a living creature. Only the most accurate 

 microscopic examination and observation of its development 

 enable us to demonstrate its animal nature. The young sponges 

 leave the body of their mother as minute ciliated larvae and swim 

 gaily about. This free life lasts several days, and then the little 

 animals attach themselves to stones or similar objects and become 

 motionless sponges. 



These few instances, and particularly a glance at our illus- 

 tration, will show that external appearance alone is not sufficient 

 to enable us to distinguish between animal and plant. Let us 

 now briefly consider the various distinctive features upon which 

 science has based the division of the organic world into two large 

 kingdoms. 



The greatest distinction is represented by the difference in 

 the process of metabolism. Whilst the animals are for their 

 nutrition restricted to organic matter, that is> other living things, 

 we have already seen that plants possess the faculty of extracting 



