300 ON THE CLASSES OF THE 



themselves on two parallel lines ; that the decapod Crus- 

 tacea have the same number of branchiae, that is, seven on 

 each side like some Cyclostomous fishes ; but that these 

 branchiae retreat further and further from the head, until 

 finally in the Onisci they reach the tail. The branchial 

 arcs of fish are supported by processes which are articu- 

 lated with the os hyoides ; and M. Latreille thinks that 

 these articulated appendages of the branchial rays repre- 

 sent the four last maxillary feet and the ten feet properly 

 so called, while the os hyoides represents the great ster- 

 num of the Crustacea. Finally, imagining that " les 

 Crustaces et les Poissons sont deux classes qui ne souffrent 

 point entre dies d'intermtdiaires" he defines a decapod 

 brachyurous Crustaceous animal, such as a Pagurus, to 

 be nothing else than a sort offish of which the opercular 

 or jugular region is aggrandized into a thorax, shut below 

 by a sternum composed of the os hyoides and covered above 

 by a shell common to it with the head ; a fish of which the rest 

 of the body has been divided into segments, and in which 

 the seven rays carrying the branchiae have gradually re- 

 treated towards the tail after receiving articulated appen- 

 dages ; a fish in which the ventral and anal fins have be- 

 come pseudo-feet, and of which the maxillae have been 

 divided longitudinally in the middle. 



I cannot help thinking, however, that in this ingenious 

 method of making out a Pagurus to be a fish, the imagi- 

 nation has been much more consulted than the eye; for, if 

 the single circumstance of the possession of external bran- 

 chiae be neglected, in no respect whatsoever does the above 

 description answer to a fish more than to many other ani- 

 mals. We come then to this question, Do not the systems 

 of circulation and respiration, though unsupported by other 



