Fissiparous Species of Tubicolar Annelid. 1 17 



appendages. 2. Such appendages modified into jaws around 

 the mouth. 3. A true heart in communication with the peri- 

 visceral cavity : that is, the Insecta,Myriapoda,Araehnida,and 

 Crustacea— we have left a large division of the animal king- 

 dom, to which the old term of Vermes might well be appro- 

 priated, had it not been already used in so many significations. 

 For this division, whose members are united by a marked com- 

 munity of structure and development, and which includes the 

 Annelida of Cuvier and a large section of his Radiata, viz., 

 the Entozoa, the Rotifera, and the EcJiinodermata, I have 

 elsewhere proposed the name of Annuloida, a term parallel to 

 that very useful one of Molluscoida (Molluscoides), invented 

 by Milne -Edwards for the Polyzoa and Ascidians* 



If it be remembered that it is only within the last few years 

 that the structure and development of these A nnuloida — which 

 present extraordinary difficulties to the investigator — have 

 been made the subjects of thorough and complete examination, 

 it will not be a matter of surprise that, at present, the subordi- 

 nate division of the group must be effected more by reference 

 to types than by exact definition. Of course this is still 

 more the case with the smaller sub-divisions ; and until much 

 more light has been thrown on these most interesting but 

 most perplexing creatures, I think it would be well to under- 

 stand the existing classes and orders to be purely conventional 

 and artificial. For my own part, I doubt greatly whether any 

 well-marked natural demarcation can, at present, be drawn be- 

 tween the Annelida (M. E.) and the Scoleidw, or between 

 these and the Entozoa ; or, again, between the latter, the 

 Turbellaria, and the Rotifera ; or, once more, between the 

 Annelida and the EcJiinodermata ; though I have little doubt 

 that the progress of inquiry will tend here, as elsewhere, to 

 eliminate osculant forms, and to substitute definitions for 

 types. 



* In writing this passage it escaped my memory that the very same division 

 had been long ago proposed by Milne-Edwards himself : 



" Je crois qu il faudrait diviser cet embranchement (Les Articules) en deux 

 groupes principaux, l'un les articules a pieds articules, et l'autre les annelides, 

 les Helminthes, les Rotateurs, &c, serie a laquelle on pourrait donner le nom 

 vulgaire des Vers." Sur la circulation dans les Annelides. Ann. des Sc. Nat.. 

 1838, p. 194. 



