268 CONTRIBUTIONS TO THE NATURAL HISTORY 



muscular partition of the lower side of the body. Fig. 13 of the same plate represents a 

 portion of the same cord freed from all the surrounding tissues, with its well-characterized 

 isolated cells of somewhat unequal size, and irregular, though chiefly linear, arrangement. 



As for the bulb when seen with the naked eye, it appears simply as a dark speck, 

 (Plate I. Fig. 5 to 11,) from which the tentacles issue. Under a moderate power, say 

 of from ten to twenty-five diameters, it appears like a crescent-shaped projecting mass, 

 (Plate II. Fig. 1 1 to 17,) thickest towards its base, thinner towards its prominent margins, 

 and varying in apparent form in consequence of the different positions which it assumes. 

 When stretched out laterally, (Plate II. Fig. 12, 14, 16, and Plate III. Fig. 14,) it is 

 almost crescent-shaped or semicircular ; and specks are noticed along its margin at the 

 base of each tentacle. The substance, also, of the bulb presents then a regular arrange- 

 ment, the pigment-cells being disposed in conical masses, with their points turned towards 

 the black dots, while their wider bases unite in a semicircular dark mass. The same ap- 

 pearance is observed, whether we look at the bulb thus stretched from above or from below. 

 The radiating cones of dark pigment-cells, however, are more distinctly seen from below, 

 as is evident from Plate I. Fig. 2, or Plate II. Fig. 12, 14, 16, and Plate III. Fig. 14, 

 when contrasted with Plate I. Fig. 3, 4. Seen from the edge in that stretched position, 

 the tentacles being bent downwards, (Plate II. Fig. 13,) the position of the tentacles, 

 which extend further inward on the upper side of the bulb than on the lower side, pre- 

 vents a correct appreciation of the structure of the bulb. The black specks, however, 

 which are placed on the lower surface of the tentacles, shine through, and form a double 

 curve of black spots, the middle of which stands higher than the lateral parts, for a rea- 

 son which will be obvious presently. If the tentacles are raised, but the bulb remain 

 in the same position, (Plate II. Fig. 11, and Plate I. Fig. 1,) the basal part of the bulb is 

 easily distinguished, and the black specks appear clearer, as they are now seen directly. 

 In this position it can easily be ascertained that the chymiferous tube is really distinct 

 from the bulb, and placed behind it, and that the nervous cord, Fig. 11, a, a, reaches the 

 bulb on its inner lower margin. 



Seen from the edge, (Plate II. Fig. 11 and 13,) the bulb appears narrower, or is not 

 so high as broad. In this position, especially when the tentacles are raised, (Fig. 11,) 

 the whole relative arrangement of parts is most distinctly seen. The chymiferous tube, 

 as well as the sensitive cord, a, a, is traced to the base of the bulb, and the somewlyit 

 triangular ganglion, c, of the base, which is faintly seen in Fig. 13, is here more strongly 

 marked. Seen from below and fully stretched out, (Plate II. Fig. 14,) the triangular 

 ganglion, d, d, is still more clearly seen, and the radiating pigment-cones most distinctly 

 noticed. The black specks. Fig. 14 and 16, a, a, a, form a curved series arising from the 



