ANIMAL KINGDOM. 301 



considerations, form a principle of affinity of sufficient im- 

 portance to authorize the connexion of Crustacea with 

 fishes ? I answer that they certainly would be sufficient for 

 the connexion of Vertebrated animals, because we see that 

 the most natural groups into which these can be divided are 

 founded on the system of respiration : but if it be possible 

 to show that the Annuhsa cannot be naturally grouped and 

 arranged among themselves, by their system of respiration 

 and circulation, then I conceive the case to be altered, and 

 that the similarity in this respect which any Annulose ani- 

 mals, as Crustacea, may bear to other animals ought not to 

 be accounted a principle of affinity unless supported by 

 other more important considerations. Now 1 would ask 

 any entomologist, whether the Pycnogonidcs do not connect 

 the Crustacea and Arachnida. If they do, as Savigny, La- 

 treille and Lamarck are all of opinion, it is exactly a case in 

 point where two groups of animals with a similar system of 

 circulation are connected together by others which possess 

 one quite different fi'om either. And this I venture with de- 

 ference to submit to naturalists, as the nature of the con- 

 nexion between Crustacea and Fishes which are linked 

 together by the Annelides and Myriapoda. 



It must however be repeated, that much investigation is 

 yet requisite before we can conclude the arrangement which 

 I have ventured to propose to be perfectly natural ; and in 

 publishing the foregoing remarks I would willingly be un- 

 derstood to imitate the caution of M. Latreille, who in a 

 supplement to the Memoire which we have just been dis- 

 cussing has expressed himself as follows : " Mes lecterns 

 toudrotit bien ne pas oublier que mon opinion, dans un svjet 

 si obscur, n'est qvHune pure hypothhe, et que "'e ne la pre- 

 sente qu'avec une extreme reserve, celle qui convient a un 



