Ixiv INTRODUCTION 



least the aquatic worms, as opposed to the parasitic worms, 

 Gordius, for instance,^ led straight to the annelids, and 

 through them to the cirrhipedes and molluscs. Other 

 aquatic worms took to the air and gave rise to the insects 

 via gnats and mayflies. Insects, adopting soHtary habits, 

 became arachnids ; and arachnids, taking once again to 

 water, became crustaceans. 



The molluscs, continuing Lamarck's exposition, led to the 

 fishes through a regular gradation of other molluscs still 

 remaining to be discovered : and the fishes to the reptiles. 

 The reptiles, he said, were differentiated by environmental 

 action into two divisions, of which one led to the birds, 

 via the chelonians or tortoises, and thence to the mono- 

 tremes ; while the other led to the Amphibian mammals 

 via the saurians, especially of the crocodile type. Of the 

 Amphibian mammals, some took to feeding on grass on the 

 sea-shore, like the walrus and manatee,^ and so brought 

 about the development of the ungulates. Others, such as 

 the seal, confined themselves to an animal diet, and thus 

 led to the unguiculates. 



§ 7. Physiology. 



On approaching a work of philosophical physiology written 

 a century ago, the point to which we look with the greatest 

 interest is the attitude of the writer towards the ancient 

 problem now bearing the modern name of vitalism. Through- 

 out last century, controversy was ever returning to that 

 great and fundamental question as to whether organic pro- 

 cesses or functions are due exclusively to the ordinary laws 

 of physics and chemistry, or whether those laws are sup- 

 plemented by others of a spiritual or non-material character. 

 When the problem is looked at with an exclusively physio- 

 logical interest, the opposite schools are referred to as vitalism 



* He referred, no doubt, to the free sexual form. 



• This is, of course, a mistaken observation. The walrus is almost or completely 

 carnivorous, while the manatee feeds exclusively on aquatic plants below the surface 

 of the water. Neither animal has the habit alleged by Lamarck. 



