OF THE ANNULOSA. 345 



Stomatopoda and Amphipoda the head is distinct from the 

 thorax. The Lamodipoda and Isopoda appear to complete 

 the group, and by means perhaps of the genus Bopyrus 

 to reconduct us to the Branchiopoda. 



Although very far from vouching for the infallibility of 

 this series of affinities, I think that the reader will, without 

 difficulty, allow that it is not in absolute contradiction to 

 the disposition of Nature. It is indeed almost the same 

 series as that laid down by ML". Latreille in the Regne Ani- 

 mal, differing only in its including those affinities which 

 he specifies as having a real existence, but which he ne- 

 vertheless neglects, or finds it difficult to employ, in his 

 method of arrangement. I shall have occasion also, here- 

 after, to support the above distribution of Crustacea by 

 other arguments ; and in the mean time I request it may 

 be understood that it is the disposition of the component 

 parts of the class, and not the limits that may have been 

 affixed to the respective orders,- — in short, that it is the 

 chain of affinity, and not the accurate designation of the 

 groups, which I would here propose to entomological no- 

 tice. Having said thus much to prevent mistake, I may 

 now proceed to state that the general character of the Crus- 

 tacea as an Annulose class consists in their breathing by 

 means of branchiae, and being in possession of a complete 

 circulation. The blood, after communicating with the sur- 

 rounding medium, passes into a great ventral vessel, which 

 distributes it over the body, whence it returns to a sort of 

 heart or muscular ventricle situated in the back, by means 

 of which it arrives again at the branchiae. Now, it is ma- 

 nifest that this is the circulation of a Fish, rather than of a 

 Mollusque, the heart of which is always aortal ; and this 

 circumstance might be adduced as conclusive evidence that 



