ON DINOPHILUS GIGAS. Ill 



coides (= D. capitata), D. metameroides, and D. cau- 

 data. From each of these the Cornish species diflPers in some 

 respect. From D. vorticoides it is distinguished by the 

 absence of a general coating of cilia on the dorsal surface, and 

 by the presence of definite " segmental '^ ciliated bands ; from 

 D. raetameroides it diflPers in the entirely superficial nature 

 of the apparent '' segmentation/^ adjacent segments not being 

 separated by infoldings of the body wall. 



I have not been able to consult Levinsen's recent description 

 of D. caudata/ but, so far as I can gather, it resembles D. 

 vorticoides rather than the present form. 



It will be seen from what follows that a further character is 

 presented by the present species, which has not been recognised 

 in others — the possession of a well-marked nervous system. In 

 the absence of any detailed information as to the structure of 

 other forms it would be premature to regard this as a specific 

 character, but even without it there seems to be sufficient 

 warrant for establishing a new species, which I propose to 

 call D. gig as, from the large size of the sexually mature 

 individuals. 



II. — Anatomy. 



In its general structure D. gig as agrees closely with the 

 D. apatris of Korschelt, difi'ering from it chiefly in the pre- 

 sence of a nervous system and in the histological structure 

 of the ectoderm. The paper of Korschelt^ is so complete, and 

 contains so full an account of the previous observations on the 

 genus, that it is unnecessary to do more than refer the reader 

 to it before passing on to a detailed description of the present 

 species. 



The ectoderm, as has already been seen, varies in charac- 

 ter in diflferent parts of the body. In the head a transverse 

 section (fig. 3) shows a well-marked diflFerence between the 

 dorsal and ventral portions. On the ventral side are seen cells 



» • Viddensk. Meddel. fra den naturh. Forea. ia Kjobenhavn,' 1879-80. 

 ^ ' Zeitsclir. f. w. Zoologie,' Bd. xxxvii, lift. 3. 



