8 BRACHIOPODA. 



Some Terebr alula which I watched for a long time 

 seemed, however, to be more active than passive in 

 feeding. They were incessantly opening and folding 

 their cirrous arms, and drawing or sucking in, by means 

 of the whirlpool thus caused, every animalcule within its 

 influence. The action reminded me of that of a Bar- 

 nacle, the only difference being in the position of the 

 arms, which in Balanus are placed in front, and in 

 Terebratula on the sides of the animal. Possibly Cuvier's 

 notion that the Brachiopods do not differ much from 

 the Cirripeds was correct, although the relationship be- 

 tween them may be one of analogy rather than of 

 affinity. Very lately Dr. Gratiolet has expressed an 

 opinion that the Brachiopods are allied to the Crus- 

 tacea in respect of their vascular system, and not to the 

 Mollusca, or least of all to the Tunicata. Milne-Ed- 

 wards has included them with the Tunicata and Poly- 

 zoa, in his Class " Molluscoida." Lacaze-Duthiers sepa- 

 rates them from the Acephala mainly on embryogenic 

 grounds, remarking that the difference in this respect 

 between the Brachiopoda and Acephala is as great as 

 between the latter and the Gasteropoda. In this contro- 

 verted and unsatisfactory state of our knowledge, it 

 would seem best to retain them for the present in the 

 great kingdom of the Mollusca, as a class of coordinate 

 value with the Conchifera, — the Pteropocla and Gastero- 

 poda forming another and equally poised group. The 

 Brachiopoda have certainly some features in common 

 with the Tunicata, as well as with the Conchifera ; but 

 they differ essentially from both in having cirrous arms, 

 in which latter respect they resemble the Cirripedia. 

 The perforated structure of their shells agrees with that 

 of the Balanidce, and also of the Polyzoa. They are con- 

 fessedly anomalous, and to a certain extent sui generis. 



