115 



discussion ut" the oi)inions which have been expressed by vurious writers make it unnecessary 

 tbr me to attempl the same lask in all its details. I may therefore limit myselt" to comments 

 on a few ot" the points which seem to me to need further discussion. 



De Selys Longchami'S concludes that P/ioronis is not nearly allied to Cephalodiscus. 

 He shews, with Iked.v and Goodrich, that Masterm.-vn's proboscis-cavities and collar-cavities in 

 Actinotrocha are not distinct spaces, but that the body-cavity is divided into two parts only by 

 the oblique septum which has universally been recognised as occurring at the base of the series 

 of larval tentacles. He recognises, however, the fact pointed out by Ikeda and confïrmed by 

 Goodrich (03) and Schultz (03, 2) that at a somewhat late stage in the development of 

 Actinotrocha, there originates a coelotnic space which lies just in front of the larval septum 

 and sends outgrowths into the permanent tentacles. In his discussion of the cavities of the body 

 he does not seem to me to take enough account of the morphological importance of this space, 

 the mode of development of which is, however, not quite certain. Goodrich (p. iii) and de 

 Selys Longchamps (p. 33) consider that it is formed as a schizocoel, while Schultz (03, 2, 

 p. 4S7, figs. 18, 19) States that in Actinotrocha, regenerating after injury, it arises as two 

 anterior diverticula of the post-septal coelomic cavity. But, however it may first originate, authors 

 are agreed in stating that it increases in relative size during the further development. At the 

 metamorphosis, when a large part of the anterior region of Actinotrocha is thrown off, the 

 remains of the praeseptal blastocoelic cavity persists as the vascular ring or rings, while the 

 praeseptal coelomic space becomes the lophophoral coelom of the adult, giving rise also 

 (Schultz, 03, 2, p. 487) to the cavity of the epistome. 



Schultz, with Fowler (92, 2, p. 297), considers that the praeseptal coelom is to be regarded 

 as the homologue of the collar-cavity of the Enteropneusta ; but he is of opinion that this 

 Enteropneust feature is only acquired with the assumption of the adult characters, the larva 

 having the significance of a Trochosphere, and not shewing any indications of "trimetamery". 

 I am inclined to accept the view that the adult lophophoral cavity is a collar-cavity, but I 

 think that the view of Schultz with regard to the significance of Actinotrocha requires some 

 modification. It may be noted that although this author recognises the second and third body- 

 cavities of the Enteropneusta in the adult Phoronis, he does not attempt to shew that there 

 is any representative of the anterior body-cavity in that animal. My own view with regard to 

 this point is intermediate between that of Masterman and that of Schultz. 



De Selys Longchamps lays stress on the distinction between the haemocoelic nature of 

 the large praeseptal cavity of Actinotrocha (which he nevertheless terms the "cavité collaire") 

 and the coelomic nature of the metasomatic or postseptal cavity. It can hardly be doubted, 

 from the relations of the larval blood-corpuscles, which lie freely in the praeseptal cavity and 

 at the metamorphosis pass into the blood-vessels, that the cavity itself has intimate relations 

 with the vascular system. But in the younger stages of Actinotrocha, the praeseptal cavity is 

 continuous with the metasomatic cavity, the septum being difterentiated first on the ventral side, 

 and being completed dorsally only at a comparatively late stage in larval life. When the septum 

 is complete, there is a postseptal coelomic cavity with a coelomic epithelium, and a praeseptal 

 haemocoelic cavity which has no complete epithelial lining. 



