NOTES ON THE ANATOMY OF DINOPHILUS. 137 



wliicli fills the general body-cavity, passing from segment to segment 

 through apertures which remain between the interlacing muscle-fibres 

 constituting the dissepiments, and finally escape from the body on 

 the ventral side of the last segment. 



The above description shows that in Protodrilus the eggs fall 

 into the general body-cavity, whilst the same is true of D. gyrociliatus, 

 where the body -cavity opens to the exterior by means of a ventral 

 pore situated near the base of the tail. The fact that in D. tseniatus 

 the interovarian cavity has been above shown to be continued 

 ventrally almost as far as the anus, taken in conjunction with the 

 admitted difficulty of discovering the actual generative pore except 

 when eggs are being laid, is distinctly in favour of the view that 

 the eggs of D. txniatiis are laid in the same manner as that which 

 has been already described in other species of Di)iophihis. The 

 analogy of D. gyrociliatus, in which the eggs undoubtedly fall into 

 the general body-cavity, further suggests that the interovarian cavity, 

 into which the ova fall in D. tseniatus, and which is continuous with 

 a passage which leads towards the exterior, is similarly a part of the 

 general body-cavity. 



On the Afiinities of Dinophilus — It has been repeatedly pointed out, 

 by Metschnikoff, Lang, Repiachoff, and Korschelt, that Dinophilus 

 has affinities with the Annelids, and more particularly with the 

 Archiannelids. Weldon (13) expresses himself even more definitely 

 in favour of the Archiannelid relationships of this form, supporting 

 his conclusions by referring to the muscular oesophageal organ, to 

 the ciliated ventral surface, associated with lateral nerve-cords, and 

 to the character of the excretory organs, as described by Meyer. 



The similarities between Dinophilus and the admitted Archiannelids 

 are so numerous and so striking that it can hardly be doubted that 

 the above conclusion is amply justified by the facts. It may, how- 

 ever, be worth while to call attention to the special resemblances 

 shown by D. tseniatus to admitted Archiannelids, and to one or two 

 considerations which are suggested by the study of this animal. 



I. External ciliation. — The existence of two rings of cilia on each 

 segment, a feature which appears to be so characteristic of D. 

 tseniatus is common to this species and to Protodrilus Leuckartii 

 (Hatschek, No. 5). In the latter animal, each segment is provided 

 with two rings, interrupted, as in Dinophilus, by the uniform cilia 

 which cover the ventral surface (ventral groove in Protodrilus) . Two 

 prgeoral rings of cilia exist in Protodrilus, which, however, differs 

 from Dinophilus in possessing an elongated " postoral region of the 

 head^' (containing the muscular appendage of the oesophagus, and 

 hence probably identical with the first body-segment of Dinophilus) 

 which bears five rinsfs of cilia. 



