174 THE PROGRESS OF DEGRADATION. 



This fact of degradation, strangely indicated in geologic 

 history, with reference to all the greater divisions of the ani- 

 mal kingdom, has often appeared to me a surpassingly won- 



in certain cases, could only be slightly traced, and with the greatest dif- 

 ficulty, in other instances. The notion thus laid down of the virtual ex- 

 istence of cranial vertebrae did not encounter very great opposition : it 

 could not be denied that there was a certain general resemblance between 

 the osseous case of the brain and the rachidian canal ; the occipital, in 

 particular, had all the characteristic features of a vertebra. But when- 

 ever an attempt was made to push the analogy further, and to determine 

 rigorously the anterior vertebrae of the cranium, the observer found him 

 self arrested by insurmountable obstacles, and he was obliged always to 

 revert to the virtual existence. 



" In order to explain my idea clearly, let me have recourse to an ex- 

 ample. It is certain that organized bodies are sometimes endowed with 

 virtual qualities, which, at a certain period of the being's life, elude dis- 

 section, and all our means of investigation. It is thus that, at the mo- 

 ment of their origin, the eggs of aU animals have such a resemblance to 

 each other that it would be impossible to distinguish, even by the aid of 

 the most powerful microscope, the ovarial egg of a craw-fish, for exam- 

 ple, from that of true fish. And yet who would deny that beings in every 

 respect different from each other exist in these eggs ? It is precisely be- 

 cause the difference manifests itself at a later period, in proportion as 

 the embryo develops itself, that we are authorized to conclude that, even 

 from the earliest period, the eggs were different, — that each had virtual 

 qualities proper to itself, although they could not be discovered by our 

 senses. If, on the contrary, any one should find two eggs perfectly alike, 

 and should observe two beings perfectly identical issue from them, he 

 would greatly err if he ascribed to these eggs different virtual qualities. 

 It is therefore necessary, in order to be in a condition to suppose that 

 virtual properties peculiar to it are concealed in an animal, that these 

 properties should manifest themselves once in some phase or other of its 

 development. Now, applying this principle to the theory of cranial ver- 

 tebrae, we should say, that if these vertebrae virtually exist in the adult, 

 they must needs show themselves in reality at a certain period of de- 

 velopment. If, on the contrary, they are found neither in the embryo 

 nor the adult, I am of opinion that we are entitled likewise to dispute 

 their virtual existence. 



** Here, however, an objection may be made to me, drawn from the 

 physiological value of the vertebrae, the function of which, as is well 

 known, is, on the one hand, to furnish a solid support to the muscular 

 contractions which determine the movements of the trunk, and, on the 



