xxxvi INTRODUCTION 



Lamarck was merely following a precedent, of which he 

 fuUy realised the inappropriateness. In his own classi- 

 fication, he strikes out a new hne, and begins his animal 

 scale with the simplest existing animals. 



The degradation noted by Lamarck as he passed along the 

 scale from mammals to infusorians is traced throughout the 

 various systems of organs. The skeleton is lost, on passing 

 the fishes ; the nervous system, on passing the insects ; 

 respiration comes to an end with the radiarians, and so on 

 with the circulatory, digestive and other systems. So, too, 

 the lungs of mammals gradually deteriorate through the birds 

 to the reptiles and fishes, where they are replaced by " less 

 perfect" respiratory organs, in the shape of gills. These 

 again vanish farther on, and give place to the still more 

 imperfect system of tracheae in the insects and arachnids : 

 while lower down the scale, respiration is entirely lost. 



The bilateral symmetry which characterises all animals 

 down to the insects similarly gives way to a radiating shape 

 in Lamarck's class of " radiarians," and these merge into 

 amorphous infusoria. Polyps represent the intermediate 

 state : for they have radiating tentacles around the mouth, 

 but are not otherwise of definite shape. Nature has, accord- 

 ing to Lamarck, just started in them that radiating form, 

 which is carried to its highest perfection in the echinoderms. 



A few observations on special points may be made before 

 I pass on to the subject of use-inheritance. Lamarck, as 

 we shall see in dealing with his physiology, assumed the 

 existence of " subtle, invisible fluids," which like spirits in 

 the past, and like vital forces or biotic energy in the present, 

 served to explain anything which remained a mystery before 

 materiahstic methods. They were useful for instance for 

 explaining the physical origin of the radiating form of cer- 

 tain animals. " The subtle surrounding fluids which enter 

 the ahmentary canal are expansive, and must by incessant 

 repulsion from the centre towards every point of the circum- 

 ference give rise to this radiating arrangement of the parts." 



In much the same way he explains why birds have feathers 



