72 ETIENNE GEOlvFROY SAINT-HILAIRE 



Geoffrey's morphological units or materials of organisa- 

 tion were in the case of the skeleton with which his 

 researches principally deal the single bones. But the 

 interesting point is that he sought his skeleton-units in the 

 embryo, and considered each separate centre of ossification 

 as a separate bone. Coalescence of bones originally separate 

 is one of the most usual events in development, and it is an 

 occurrence which, more than any other, tends to obscure 

 homologies. Because of its coalescence with the maxillaries, 

 the intermaxillary in man was not discovered until Vicq 

 d'Azyr and Goethe found it separate in the embryo. 

 Apparently quite independently of Goethe, Geoffrey hit 

 upon this plan of seeking in the embryo the primary 

 elements or materials of organisation. In an early paper on 

 the skull of Vertebrates, 1 where he is concerned with showing 

 that each bone of the fish's skull has its homologue in 

 the skull of higher Vertebrates, he is faced with the difficulty 

 that the skull of the fish has more bones than the skull 

 of higher Vertebrates. " Having had the inspiration," he 

 writes, ">to reckon as many bones as there are distinct centres 

 of ossification, and having made a consistent trial of this 

 method, I have been able to appreciate the correctness of the 

 idea: fish, in their earliest stages, are in the same conditions 

 relatively to their development as the fetuses of mammals, 

 and hence bear out the theory " (p. 344). So, too, in dealing 

 with the homologies of the sternal elements (snprn, p. 57) 

 he treats as separate bones the " annexes " of the sternum 

 in birds, though these are separate only in the young. 



If the same materials of organisation are present in all 

 animals, and if they are arranged always in the same 

 positions relatively to one another, how does it come about 

 that animal forms are so varied, what explanation can be 

 offered of the diversities of organic structure? Geoffrey's 

 main answer to this question is his Loi dc balancement. The 

 law was enunciated by him already in 1807.- \Ye take the 

 following quotation, which represents his thought most 

 nearly, from the Conrs dc riiistoirc natiircUc </,'s Mauuni- 

 fcres (1829). "According to our manner of regarding the 



1 Ann. Mus. </ ' I fist, nut., x., pp. 342-65, 1807. 

 '-' he. cif., x , p. 343. 



