THE BRITISH FOSSIL BRACHIOPODA. 313 



take the digestive tube : sections of larvae of Chastopods (for example Nerine) show that 

 the intestinal canal is immediately applied to the dorsal wall of the body, exactly as in a 

 larva of a Brachiopod ; and in the adult condition this canal is fixed by two mesenteries . 

 the one ventral, and the other dorsal, absolutely as in the adult Brachiopod. The muscular 

 system offers us, besides some dissimilarities, marked analogues. If Kowalevsky has been 

 unable to trace, either in the larva of the Brachiopod or in the adult animal, the 

 homologues of the circular muscles of worms, on the other hand he has seen that the 

 muscles which pass to the bristles in the larva of the Brachiopod, and which at 

 a later period become the occlusors, have their homologues in Worms; likewise the 

 ventral muscles of the larva, which later on are transformed into peduncular muscles, and 

 the dorsal muscles of the peduncle, have, as homologues, the ventral and dorsal muscles 

 of Worms. As to the divaricators, it is difficult to find for them homologues in the 

 muscles of Worms, unless, however, they correspond to the muscles of the segments of 

 the Worms, the more so since they are always situated on the posterior side of the 

 thoracic segment. The Russian author abstains from endeavouring to establish any 

 comparison with respect to the nervous system of the Brachiopod and the Worm. 



" We find the same analogies in the genital organs, the structure of the ovaries, 

 suspended by the aid of a mesentery, and the shape of the oviducts, all so similar to the 

 segmented organs of Worms ; all these characters indicate a relationship between the 

 two types. With respect to the branchiae, we have seen that they are always formed on 

 the dorsal side of the mantle ; one might therefore, perhaps, homologize them with the 

 dorsal branchiae of the Dorsibranchiates (Eunice, Nerine). On the other hand, as in 

 Thecidium, the cephalic segment enters into the formation of the branchiae. These 

 last might, perhaps, be homologues of those of the Cephalobranchiates ; anyhow, this 

 differentiation has no importance, and in both cases, whether they are dependencies of 

 the head or of the mantle, one can always compare them with the branchiae of Annelid 

 Worms. 



" The most embarrassing part is the shell, for the tubes that envelope tubicolous 

 worms cannot be assimilated to it, as they are completely independent of the body of 

 the animal. There exist, however, certain analogies between the tubular canals of the 

 shell and the integument of the Worm ; likewise, the prolongations of the mantle which 

 fill these canals present, after the dissolution of the shell in acid, a great resemblance 

 with the prominences which are seen in the gelatinous and subcutaneous layer of 

 Chlorcema. In every respect, therefore, the Brachiopods approach the Worms ; but it 

 remains to be determined whether they should form an order or a separate class of 

 Worms. Kowalevsky believes that they are not sufficiently distinct from the annulated 

 Annelida to be separated from them ; and after having weighed all the arguments for 

 and against, he says that he believes that the Brachiopoda should be considered simply 

 as an order of Annelida, as they present at least as much resemblance to the Chcetopodes 

 as the Discop/iores." In this opinion I am unable to concur. 



