ON THE CLASSES OF THE 



esprit sage et toujours pret a revenir sur ses pas, lorsqu'il 

 reconnaitra son erreur. Entre le poisson dont I 'organiza- 

 tion est la plus simple et le crust ace le plus parf ait sous ce 

 rapport, il existe, ainsi queje Vai dit dans mon memoire, 

 un hiatus qiCilnous est maintenant impossible de remplir, 

 Quand bien mime on admettrait avec moi que les lamproies 

 et les gastrobranches sont les dernier s de la classe de&poissons, 

 la fornix et la situation de leur colonne vertebrate ne pour- 

 raient pas itre comparees avec la motile epinilre des Crus* 

 taces" 



But if we agree with MM. Cuvier and Lamarck that the 

 Annelides come nearer to the Vertebrated animals than to 

 the Crustacea or indeed any Annulosa, it may still be asked, 

 how we would account for the singular circumstance of 

 the Crustacea possessing a system of circulation and bran- 

 chiae resembling those of a Vertebrated animal. Now 

 M. Latreille has given me the answer to this question 

 himself, by bringing these animals into comparison with 

 the Amphibia, and by assimilating the Arachnida to 

 some of the Reptilia, — both analogies, I confess, which 

 I should never of myself have thought of; but the 

 statement of them by so great a naturalist has served to 

 convince me that what in reality is only a relation of ana- 

 logy has been mistaken for a relation of affinity. This is 

 so common a cause of delusion in the investigation of na- 

 tural affinities, that I shall be obliged to return to a fuller 

 consideration of it in the following chapter, where the 

 mischief it has occasioned will be more perceptible ; 

 and in the mean time shall only observe that the Crustacea 

 possess a system of circulation and respiration analogous 

 to that of the Amphibia; that like these they are fond of 

 water, but can subsist for some time out of it ; that some 



