386 LOWEST ORDERS OF ANIMALS. 



mammal. A slight investigation will convince us that 

 this view has no foundation. Although a certain re- 

 lationship may be found between some of the members 

 of one class, and those of the other immediately joining 

 it, yet this is equally discovered to exist towards 

 classes more remote from each other ; and in no one 

 instance can we detect anything like the passage of an 

 animal of one class into an animal of another. Until 

 this is done, we cannot but regard the forms of animal 

 life as distinct creations, each one fitted for its state of 

 being, springing from the command of the great First 

 Cause.* 



But it is time to quit these speculative questions, and 

 proceed to the examination of the general conditions of 

 animal life at the present time. 



Lowest in the scale of animals, and scarcely distin- 

 guishable from a vegetable, we find the sponge, attached 

 to and passing its life upon a rock, exhibiting, indeed, 

 less signs of feeling than many of the vegetable tribes. 

 The chemical differences between vegetables and sponges 

 are, however, very decided ; and we find in the tissues 

 of the sponge a large quantity of nitrogen, a true animal 

 element, which exists, but in smaller quantities, in 

 vegetables. 



These creations, standing between vegetable and 

 animal life, possess the singular power of decomposing 

 carbonic acid, as plants do ; and the water in which they 

 live always contains an excess of free oxygen. 



The polypes are a remarkably curious class. " Fixed 

 in large arborescent masses to the rocks of tropical seas, 

 or in our own climate attached to shells or other sub- 

 marine substances, they throw out their ramifications in 

 a thousand beautiful and plant-like forms ; or, incrusting 

 the rocks at the bottom of the ocean with calcareous 

 earth, separated from the water which bathes them, they 



* The Vestiges of the Natural History of Creation. 



