I 19 



of CcpJialodiscus\ althoug-h if any such rclation did exist it could hardly mean more than diat 

 the faculty of secreting a tube was fonnerly possessed l)y the epidermis generally. It may be 

 noted that in Balanoglossus a "tenacious tube" is formed by mucus secreted by the epidermis, 

 and that the surface of the proboscis and of the collar at least are concerned in the secretion 

 of this tube (Morgan, 94, pp. 17, 19). 



In the budding processes of Cephalodiscns the coelomic cavities are almost certainly 

 formed by the segmentation of a space derived from the virtual metasomatic cavity of the stalk. 

 In Phoronis Schultz (03, i, p. 409; 2, p. 487) states that the cavity of the lophophore, the 

 suppo.sed collar-cavity, is an outgrowth of the metasomatic coelom, both in normally developing 

 larvae and in adults and larvae which are res^eneratinof after artificial section. 



Üne of the most striking features in which Cephalodiscus differs from Balanoglossus is 

 the approximation of the anus to the mouth ; and it can hardly be doubted that in CepJialodiscus 

 and Phoronis the short line between the mouth and anus represents the dorsal surface. It is 

 not impossible that the adult relations found in Cephalodiscus may be the result of ontogenetic 

 processes similar to those which occur in the metamorphosing Actinotrocha. It is unfortunate 

 that the study of the embryos found in the coenoecium has thrown no light on this point; but 

 on the contrary the buds of C. dodecalophus (PI. XIII, fig. 181) may give some clue to the 

 manner in which the flexure of the alimentary canal has arisen. 



In conclusion I may express the opinion that while Phoronis is not closely related to 

 the Pterobranchia, its affinities are really in that direction; and that conclusion I have tentatively 

 adopted in my article " Hemichordata" in Vol. VII of the 'Cambridge Natural History' (04). 



(IV) Relations to other animals. 



It would be going too far afield to discuss all the possible relationships oï Cephalodiscus^ 

 and for a general consideration of this question I must content myself with referring to the works 

 of ScHiMKÉwiTSCH (93), Masterman (96, I, 2; 98, i) and Delage and Hérouard (97, 98). 



Masterman (96, i) has instituted a group Trimetamera, which includes the Hemichordata, 

 the Echinodermata, the Brachiopoda, the Chaetognatha, the unarmed Gephyrea (with Phoronis)^ 

 the Polyzoa and possibly the MoUusca, while he assumes that the Chordata diverged from the 

 ancestral line which culminated in the Hemichordata. Schimkéwitsch (93) had previously expressed 

 the same idea with regard to all these groups except the Mollusca, but he did not suggest 

 any name for the assemblage. 



If Phoronis be related to CepJialodiscus, the question naturally arises whether the Sipun- 

 culoid Gephyrea have affinities in the same direction. I may here refer to a paper by Shipley 

 (90), who gives a diagram (fig. 32) of the lophophore of Pliyscosonia which is strikingly .similar 

 to my own diagram (PI. XII, fig. 159) of Cephalodiscus. The lophophore oï Physcosoma consists 

 of a crescent, placed on the dorsal side of the mouth, with its concavity facing the anus. It 

 bears a small number of short tentacles, which are provided, as in Cephalodiscus, with ciliated 

 groeves on the sides corresponding with the outer or convex side of the crescent. Its dorsal 

 ends are connected with a crescentic lower lip in precisely the same way as that in which the 

 arms of Cephalodiscus join the operculum. The so-called "vascular system" is a closed space 



