REPORT ON CEPHALODISCUS DODECALOPHUS. 11 



this indicates the central nervous system. The hjqDoderm of the basal region contains 

 numerous granular masses (gland-cells and pigment) which have a brownish hue by trans- 

 mitted light. The plumes (PI. II.) are nearly of uniform size, and consist of a thickish 

 central stem, occasionally slightly crenate, and furnished with a series of longitudinal 

 fibres ; while distally each is terminated by a peculiar bulbous enlargement, which at first 

 sight resembles the tip of certain hydroid tentacles {e.g., Coryne or Syncoryne) bristling 

 with dart-ceUs and pigment. The rugose appearance, however, is due to large gland-cells 

 containing granules and globules (PI. V. fig. l), which are arranged in a somewhat regular 

 manner round a central cavity, and which present a deep yellowish tint in the preparations. 

 This structure may perhaps be a further and special development of the somewhat large 

 hypodermic granules of the tips of the pinnae. The appearance of these bulbous enlarge- 

 ments in section is shown in PL IV. fig. 3, part of the upper wall of the stem in this 

 case being formed of the ordinary hypoderm below the tip. When the latter is cut 

 longitudinally, the space in the centre of the bulbous extremity is found to be continuous 

 with a similar space at the end of the arm. Very soon, however, transverse bridles and 

 fibres occupy the central region of the latter, so that a kind of meshwork takes the place of 

 a canal. In transverse section the terminal region of the stem is formed of a thick coating 

 of hypoderm (probably in life covered by a ciliated cuticular layer) somewhat regularly 

 marked (PI. IV. fig. 4) by strise so that the cell-like divisions are frequently wedge-shaped. 

 The hypoderm abuts on a basement-tissue, apparently continuous with that which belongs 

 to the basal apparatus next the disk, and which is in relation laterally with the axes of 

 the pinnae on each side. The wall of the canal of the arm, even in this region, presents 

 a series of fibres which render it hirsute in section, but they do not in every case meet 

 across the lumen. As we proceed downward, however, the sections of the arms are 

 flattened and the margins prominent, so as to form ventral grooves, and the two sides are 

 bound together by transverse fibres, a median junction especially being conspicuous. 

 This meshwork of fibres is better seen in good horizontal and longitudinal sections of the 

 plumes, in which the transverse fibres pass from side to side in almost parallel series, 

 minute nuclei or corpuscles being everywhere abundant, apparently adhering to the fibres, 

 or perhaps indicating their origin from cells of the connective tissue. As in the basal 

 region, therefore, the centre of the arm is composed of a series of reticulations or meshes. 

 The hypoderm also of the arm below the terminal region is considerably thinner, showing 

 that this system of lacunae reaches its culminating point in the termin.al enlargement. 

 The longitudinal fibres inside the basement-tissue are probably those observed in the 

 external views of the arms. 



The sides of the stem (PI. IV. fig. 1) are rendered plumose by a large number of long 

 slender filaments having rounded or slightly bulbous extremities, which show a linear 

 streak from base to apex, from the presence of the axis or skeleton. The latter was first 

 clearly discriminated as a " skeleton " in Cephalodiscus by Professor Eay Lankester, for 



