REPORT ON CEPHAL0DISCI7S DODECALOPHUS. 47 



6. Previous observers (M'Intosh, Lankester, &c.) have been led to assume the affinity 

 of Phoronis to Cephalodiscus and Rhabdojjleura, this conclusion being based on such 

 features as the relations of the adult lophophore to the mouth and anus. 



It must be noted, on the contrary, that Phoronis is not known to possess any repre- 

 sentatives of the notochord, gill-slits, collar-pores, and proboscis-pores of Cephalodiscus, 

 whilst there is no evidence of the existence of a collar body-cavit}^ in the former. It 

 appears to me that a renewed consideration of Phoronis, anatomically and development- 

 ally, can alone settle the question of the possibiUty of an affinity between it and Cephalo- 

 discus. 



The remarkable larva of Balanoglossus described by Weldon {loc. cit., fig. 3) is in 

 some of its features by no means unlike Actinotroeha. Such features are the general 

 form of the prae-oral lobe and trunk, the absence of the notochord and gill-slits, and the 

 existence of only three diyisions of the body-cavity. These are (I) the unpaired cavity 

 of the prse-oral lobe, and (2) the two cavities of the trunk-region. In the absence 

 of these cavities and of the notochord and gill-slits Actinotroeha dififers from the 

 larval Balanoglossus described by Bateson. It cannot, however, be denied that the dif- 

 ference between the tentacles of Weldon's larva and those of Actinotroeha is very 

 considerable, if not fundamental. 



The relation between Cephalodiscus and Rhabdopleura is in need of further elucida- 

 tion. In spite of the great resemblance between the lophophores and epistomes of the 

 two genera, many of the most important structures found in Cephalodiscus axe not known 

 to exist in Rhabdop)leura, and there does not at present appear sufficient justification for 

 the removal of Rhabdopleura to the Hemichordata, although the balance of evidence 

 might perhaps be in favour of so doing. 



I do not think that the above considerations are in any way calculated to strengthen 

 the view that Phoronis and the Polyzoa are nearly related. The result of the examina- 

 tion of Cephalodiscus appears to me to show that this genus (and Rhabdopleura also ?) 

 must be entirely removed from the Polyzoa. If this is the case, it is obvious that any 

 affinity which may be shown to exist between Cephalodiscus and Phoronis can in no way 

 affect the question of the relationship of the latter to the Polyzoa. 



