292 ON THE CLASSES OF THE 



so much science with so much ingenuity and evident zeal 

 for the truth, as must necessarily, on a first reading, dis- 

 pose every one to adopt his doctrines. The line of argu- 

 ment he pursues is very simple, and perhaps on that ac- 

 count the more seducing. He supposes it to be unques- 

 tionable that there are two distinct series of Unvertebrated 

 animals, which each meet the Vertebrata at the points 

 where these are the least organized, and where they them- 

 selves have the most complex structure. He considers it 

 undeniable that the Cyclostomous fishes are the least or- 

 ganized of the Vertebrata, and that the Cephalopoda and 

 Crustacea are each at the head of a series of unvertebrated 

 animals, and therefore concludes that the Cephalopoda and 

 Crustacea meet the Vertebrata among the Cyclostomous 

 fishes. Thus the great aim of his Memoir e becomes to dis- 

 play to the view those analogies which the Crustacea in 

 preference to the Coleoptera possess with fishes. It need 

 scarcely be mentioned that we have already arrived at 

 several of these positions by tracking closely the vestiges 

 of affinity ; we have, for example, ascertained that there 

 are two series of Unvertebrated animals; that the Cepha- 

 lopoda are at the head of one of these, and that the Cy- 

 clostomous fishes are among the least organized of the 

 Vertebrata. And yet I hesitate in giving full assent to 

 M. Latreille's conclusions, because I find the above facts 

 mixed up with an antiquated notion, which if hitherto 

 seldom questioned has also never yet been proved. Thus 

 it is a mere assumption to say that the Vertebrata are met 

 by the Annulose series at the point where this is most per- 

 fectly organized. Cuvier and Lamarck both think differ- 

 ently, as appears by the place which they have assigned 

 to the Acephalous Annelides before all white-blooded ar-* 



