1 14 



(II) Relations to the Enteropneiista. 



The resemblances of Ccphalodiscus to Balanoglossus have been confirmed by several 

 workers who have had the op])ortunity of studying sections of the former animal; and particularly 

 by Masterman (96 — 03) and Spengel (93, pp. 721, 753). Lang (90) has accepted the same 

 conclusion, and has given reasons for regarding Ccphalodisais as a Balanoglossus-like form 

 which has been specially modified in connexion witli its sedentary and tubicolous habits. Ehlers 

 (90, ]i. 164) on the contrarj' denied the affinity of Cephalodiscns to Balanoglossus. 



It seems to me hardly necessary to discuss this question further. If any weight is to be 

 attached to morphological resemblances it must be concluded that Ccphalodiscus is related to 

 Balanoglossus. When account is taken of the differences between the e.\ternal form, the size, 

 and the habits of the two types, it is indeed extraordinary that .so many of the anatomical 

 peculiarities of Balanoglossus should reappear in Cephalodiscns. As facts confirming the relationship 

 of the two forms, but not known at the time of the ])ublication of the "Challenger" Report may 

 be mentioned, — the existence of a pericardium, and probably of a glomerulus, in Ccphalodiscus; 

 the discovery, by M.\stermax, of a vascular system in the same animal: and the resemblances 

 of the embryos of Ccphalodiscus, so far as I have been able to make out their structure, to 

 those of Dolichoglossus koivalevskii. 



It cannot, however, be disputed that in spite of the resemblances, Ccphalodiscus differs 

 from Balanoglossus in various particulars which are so obvious as not to require mentioning. 

 But the general result seems to me clear, namely that Ccphalodiscus and Rhaddopleura, 

 constituting the Pterobranchia or y\s[jidophora, must l)e included, with the Enteropneusta, in 

 a larger group, for which I acrejjt B.vteson's name Hemichordata. 



(III) Relations to Phoronis. 



Here we are on much more controversial ground. The hypothesis of the affinity of 

 Phoronis to the Pterobranchia has been accepted by a certain number of authors, among whom 

 I may mention Lankester (85), Masterman (96—00), Schimki^witsch (93), Del.\ge and Hi^rouard 

 (97), RouLLv (01, p. 226), and Scmultz (03, i, 2); but it has been rejected by many others. 

 Masterman's comparisons of Actinotrocha with Ccphalodiscus and the Enteropneusta have 

 unfortunately been vitiated by the mistakes into which he appears to have fallen with regard 

 to the structure of Actinotrocha, as shewn 1)\ the concurrent testimony of Ikf.da, (iooDRiCH. 

 and DE Selys Longchamps. Schultz (03, i, p. 414: 03, 2, p. 489), while accepting the verdict 

 of these authors with regard to the facts, believes nevertheless in the affinity of Phoronis to 

 Jialanoglossus, and expresses his conviction that evidence of this relationship is to be found 

 more in the .structure of Phoronis than in that of its larva. He bases his conclusions on the 

 result of a study of the regenerative processes of Phoronis, whether after the spontaneous loss 

 of the tentacular end of the animal or after artificial section ; and on the study of regeneration 

 in .Actinotrocha after section, lie liiuls that regenerative processes are capable of giving valuable 

 aid in the elucidation of phylogenetic problems. 



Dk Selys Longchamps (04) has just published an important memoir on the structure 

 and metamorphosis of Actinotrocha. The full bibliography which he has given, and his careful 



