66 



NATURAL SCIENCE. 



July, 



position of the anus on the dorsal side, not far from the mouth, and 

 the production of the collar-region into the twelve tentacular arms 

 which have already been alluded to. The proboscis-cavity opens to 



the exterior by a pair of pro- 

 boscis-pores, which perforate 

 the nervous system. The 

 collar-cavities communicate 

 with the exterior by a pair of 

 collar-pores, which are situa- 

 ted in the immediate neigh- 

 bourhood of a pair of gill-slits. 

 The central nervous system is 

 situated in the dorsal region of 

 the collar, and it is outside the 

 basement-membrane of the epi- 

 dermis. The narrow stalk of the 

 proboscis is strengthened by a 

 tubular notochord {nch.) extend- 

 ing forwards from the pharynx. 



Fig. 8. — p. proboscis; c. collar; tr., trunk 

 or body ; al., alimentary canal. 



If the above description is really accurate, there can be little 

 doubt with regard to the affinity of Cephalodiscus to Balaiwglossus, 

 however dissimilar the two animals may at first appear. It is 

 important to notice that confirmation of the account pub- 

 lished in the " Challenger " Report has appeared from more than one 

 side. 



Should Cephalodiscus and Rhabdopleiira be really related to 



Balanoglosstis, the presumption is that they have nothing to do with 



the Polyzoa, a group in which they were temporarily placed. It 



might have been hoped that the study of Phoronis afforded by the 



" Challenger " material would have had some bearing on this question. 



But in spite of the anatomical account of P. buski, Mcintosh, the 



new species described in the Report, and in spite of the more recent 



and fuller accounts of the anatomy of the genus, published by 



Benham and Cori, the affinities of Phoronis cannot be said to be at 



all clearly known. It is by no means impossible that this animal is 



related to Cephalodiscus ; and some considerations suggesting an 



affinity between the two animals were brought forward in the 



" Challenger " Report. But the resemblances are too uncertain, and 



the differences too obvious to place the conclusion on the same level 



of probability with the conclusion that Cephalodiscus is related to 



Balanoglossus. It cannot be too strongly urged that Cephalodiscus and 



Rhabdopleura belong to Bateson's group of the Hemichordata, and that 



they have nothing to do with the Polyzoa. Phoronis may or may not 



come in the same group, but the question should not be obscured by 



the assumption, at present not sufficiently warranted, that it necessarily 



has affinities in the direction of the Polyzoa. 



S. F. Harmer. 



