OF CONCHOLOGY. 51 



would transport the Brachiopods and Polyzoa. We do not sup- 

 pose that under this head he includes the Scolecid worms, 

 although he has borrowed a few characters from them to com- 

 plete his catalogue of supposed affinities. He has distinctly 

 specified this as the group of which the Brachiopods are a mere 

 subdivision, and hence cannot call upon us to prove that they 

 are not also a subdivision of the Scolecida,* if that were pos- 

 sible. 



Class ANNELIDA. 

 =Polychosta, Oligochceta and Gephyrea. 



Animals of elongated form, characterized by a successive repe- 

 tition of pairs of similar organs or single organs representing 

 pairs, enclosed in a muscidar tunic, apart from the true skin, 

 which is or is not differentiated into segments (corresponding to 

 the successive groups of organs) by successive constrictions and 

 internal dissepiments. 



Nervous system consisting of two median cords (separated or 

 combined throughout the greater part of their extent) connecting 

 a series of subabdominal ganglia, from which nervous filaments 

 are given out, each ganglion corresponding to a segment, if seg- 

 mentation or repetition be exhibited ; these cords are united above 

 the oesophagus, near or in front of the oral aperture ; connected 

 or non-connected by a suboesophageal nerve. 



Circulation without vessels of any kind, or without a differ- 

 entiated heart, when contained within closed vessels, in which 

 case there is usually a dorsal vessel. Blood colored or uncolored. 



Branchiae external, internal or wanting; attached either at 

 the anterior or the posterior extremity. 



Genitalia usually repeated in every segment after the first few 

 anterior segments. Monoecious or dioecious ; with or without 

 copulatory organs. 



Reproducing by ova or fission; frequently exhibiting two or 

 more sexual forms. 



Absolutely free from any organic connection with extraneous 

 objects, but often forming tubes of sand, mud or calcareous mat- 

 ter, or occupying the vacant receptacles of other animals. 



With or without fasciculated chitinous setae of varied form ; 

 with or without a "segmental organ;" with or without eyes, 

 with or without " porenkanale" 



* It is hardly to be supposed that Professor Morse is opposed to 

 the course of all modern students of the group, and would, in opposi- 

 tion to their views, unite the Scolecids with the Annelids in one hete- 

 rogeneous class. 



