EEPOET ON CEPHALODISCUS DODECALOPHUS. 2t 



the preparations being somewhat semicircular and of considerable thickness. These fibres 

 pass backwards (causing the ridge on the ventral surface in contraction) towards the 

 pedicle, which they enter, filling the central space. In transverse section the appearance 

 of the latter varies, but in the best preparations a certain uniformity is observable 

 (PI. IV. fig. 5), viz., beneath the uniformly rounded hypoderm a median fold occurs 

 in the basement-tissue dorsally, while a much larger and wider one occurs ventrally, 

 and at each side of this an inner longer and an outer shorter process exist. The whole 

 has a symmetrical appearance. Such an outline would indicate that the basement-tissiie 

 was elastic and that no circular muscular fibres existed, and indeed from the descriptions 

 of Vogt and other authors similar elastic tissues subserve the function of cucular fibres 

 in Loxosoma. In some sections of unstained examples the thick basement-tissue had 

 a somewhat different aspect (PI. VII. fig. 2), probably from the condition after 

 immersion in spirit ; this, however, was exceptional. A layer of fine longitudinal fibres 

 lies on the inner surface of this coat, and from it numerous transparent an<] somewhat 

 gelatinous fibres of connective-tissue pass to the central area, which contains large 

 structures deeply stained and almost resembling gland-cells, but which appear to 'be 

 sections of the long mobile muscular fibres continued from the fundus of the body into 

 the pedicle. The close approach made by these to the " muscular baud of closelv-set 

 fusiform cells " described by Lankester in the stalk of Rhabdopleura is noteworthy ; 

 they probably represent a further development of that tissue — in which the cells have 

 disappeared. A similar series of muscle-cells in the axis of the stalk is described by 

 Harmer in his valuable paper on Loxosoma} In contraction the transverse wrinkles of 

 the basement-tissue are so close that they resemble a circular muscular coat. 



No distinct canal is thus observed in the centre of the pedicle throughout its length. 

 Towards the tip, however, certain spaces containing what appears to be a coagulable fluid 

 occur, and also globules and granules, as explained in connection witli x\\v Imds. 



The pedicle in Cephalodiscus is thus evidently a development of the body-cavity, 

 which in the young bud freely opens into its upper region. It differs, therefore, from 

 the soft stalk of Rhabdopleura, first so clearly described by Professor Allman, for that 

 has no connection with the body-cavity in the adult ; yet as the development of both 

 forms is unknown a little reservation is necessary, especially as it also contains muscular 

 fibres in Rhabdopleura, and gives rise to the buds and branches. The fibres of the stalk 

 in Rhabdopleura, according to Professor Sars, proceed "rather high up on the ventral 

 side," and '-'over the skin which encloses the digestive apparatus. Its VLUtral fil)rous 

 part may stUl be traced (see fig. 15) a considerable distance forwanl in tiie'fonnofa 

 rather wide, clear, skin-border which gradually disappears in front of the cardia. In 

 this skin-border the fine longitudinal fibres may still be distinctly observed diverging like 

 radii, but I was not able to trace their course further."- The arrangement of the parts 



' Op. eU.. p. i9. » Op. cit., p. 10. 



