302 Evolution and Adaptation 



in the chain that connects, without interruption, the older 

 inhabitants of the earth with animals living at the present 

 time. Without positively affirming that this is the case, he 

 did not hesitate to state that a transformation of this sort 

 seemed possible to him. He said: " I think that the process 

 of respiration constitutes an acquirement so important in the 

 ' disposition ' of the forms of animals, that it is not at all 

 necessary to suppose that the surrounding respiratory gases 

 become modified quickly and in large amount in order that 

 the animal may become slowly modified. The prolonged 

 action of time would ordinarily suffice, but if combined with 

 a cataclysm, the result would be so much the better." 



He supposed that in the course of time respiration becomes 

 difficult and finally impossible as far as certain systems of 

 organs are concerned. The necessity then arises and creates 

 another arrangement, perfecting or altering the existing struc- 

 tures. Modifications, fortunate or fatal, are created which 

 through propagation are continued, and which, if fortunate, 

 influence all the rest of the organization. But if the modifica- 

 tions are injurious to the animals in which they have appeared, 

 the animals cease to exist, and are replaced by others having 

 a different form, and one suited to the new circumstances. 



The comparison between the stages of development of the 

 individual and the evolution of the species was strongly im- 

 pressed on the mind of Geoffroy. He says : " We see, each 

 year, the spectacle of the transformation in organization from 

 one class into another. A batrachian is at first a fish under 

 the name of a tadpole, then a reptile (amphibian) under that 

 of a frog." "The development, or the result of the trans- 

 formation, is brought about by the combined action of light 

 and of oxygen ; and the change in the body of the animal 

 takes place by the production of new blood-vessels, whose 

 development follows the law of the balancing of organs, 

 in the sense, that if the circulating fluids precipitate them- 

 selves into new channels there remains less in the old 



