

CHAPTER VI 



The Peopling of the Open Sea, the Ocean Depths, and 



the Land Masses 



|"F every living creature in the open sea, the ocean depths, 

 -*- and on the continents were to be destroyed, those 

 organisms still inhabiting the shore would suffice for us to 

 establish quite unmodified all these doctrines constituting 

 what is now called the zoological philosophy. It is true that 

 important culminating points would be missing ; Botany, reduced 

 to the history of the Algae and a few of the lower Fungi, would 

 have been greatly simplified. We should know nothing of 

 Arachnids, Myriapods, or Insects, and the wonderful blossoming 

 of lower forms into Reptiles, Birds, and Mammals would have 

 remained unknown. But the existing littoral forms would none 

 the less have furnished us with a continuous series in which each 

 form would have been explicable in terms of the others, 

 so that it would have been possible, through their comparative 

 study, to reconstruct the conditions essential to the evolution 

 of life. The fauna of the open sea and the ocean depths, and the 

 fauna of the solid earth, on the other hand, is full of gaps. 

 In the open sea, as well as along the coasts, there are, no doubt, 

 numerous microscopic swimming creatures which belong to 

 both kingdoms : the Diatoms and the minute Algae which draw 

 their nourishment from gases of the air and water combined 

 by the sunlight, and the Protozoa which live on these 

 microphytes. After these, however, comes a series of lacunae, 

 and whole classes are absent, or represented only by specially 

 adapted types, occasionally developed from forms normally 

 fixed to the ground. The Sponges are absent, and the order 

 of Polyps is represented only by the Medusae, in which tachy- 

 genesis has replaced the phase of fixation in the polyp type 

 by a direct development ; by Siphonophora which have 

 found a means of attaching themselves to an air-bubble 

 instead of to the ground ; and by the floating Actiniae, with 



