STEREOGNATHUS. 349 



A knowledge of the physiological conditions governing the 

 relations of the contents of the cavities of bones to the flight 

 and other modes of locomotion in birds, both enabled the 

 writer to infer from one fragment of a skeleton that it belonged 

 to a terrestrial bird deprived of the power of flight, and to 

 predict that such a bird, but of less rapid course than the 

 ostrich, would ultimately be found in New Zealand.* 



Certain coincidences of form and structure in animal 

 bodies are determined by observation. By the exercise of a 

 higher faculty the reason, or a reason, of these coincidences is 

 discovered, and they become correlations ; in other words, it is 

 known not only that they do exist, but how they are related 

 to each other. In the case of coincidences of the latter kind, 

 or of "correlations" properly so called, their application to the 

 reconstruction of an extinct species is more easy and sure 

 than in the case of coincidences which are held to be constant 

 only because so many instances of them have been observed. 

 The application of the latter kind of coincidences is limited 

 to the actual amount of observation of them. 



The consciousness of that limitation led the enunciator of 

 the law of correlation to call the attention of palaeontologists 

 expressly to the extent to which it could then be applied, as, 

 for instance, to the determination of the class, but not the 

 order ; or of the order, but not the family or genus, etc. ; and 

 to caution them also as to the extent of the cases in which, 

 the coincidences being only known empirically, he enjoins 

 the necessity of further observation, and of caution in their 

 induction. Cuvier expresses, however, his belief that such 

 coincidences must have a sufficient cause, and that cause once 

 discovered, they then become correlations and enter into the 

 category of the higher law. Future comparative anatomists 

 will have that great consummation in view, and its result, 

 doubtlessly, will be the vindication of the full value of the 



* Transactions of the Zoological Society, vol. iii., p. 32, pi. 3. 



