276 CONTRIBUTIONS TO THE NATURAL HISTORY 



but, in addition to them, smaller bundles arise, which follow, in a rather less regular ar- 

 rangement (Fig. l,h,h ; Fig. 2, e,e,€), the direction of the vertical tubes, and terminate 

 (Fig. ^, g,g) above the sensitive buds. 



The general position of the two specimens, Fig. 1. and Fig. 2, must explain the great 

 difference in their appearance. In Fig. 1, which is an absolute profile, we face the in- 

 terval between two vertical chymiferous tubes ; and the two other tubes, being precisely 

 in the same position on the opposite side of the body, are not introduced at all in the 

 drawing. In Fig. 2, on the contrary, which is slightly inclined upon its base, in order 

 to show the lower partition, and to bring out the upper crown of fibres as a continuous 

 ring, we face, in the middle, one of the chymiferous tubes, and have another opposite 

 to it, also in the middle, on the other side of the body ; and at right angles with this, two 

 other tubes, one to the right and the other to the left ; and the spaces between two vertical 

 tubes appear everywhere foreshortened. Fig. 1 of Plate III. is nearly in the same position 

 as Fig. 1, Plate I., with this difference, that, being absolutely in profile, the other 

 pair of vertical tubes is not seen at all. The corresponding parts of Fig. 2 would form an- 

 gles of forty-five degrees with those of Fig. 1, if projected upon the same plane. 



On investigating closely the arrangement of these fibres, it is found that they do not 

 extend in a straight course from the upper part of the sphere to its lower margin, but 

 diverge into the arched bundles above, and in their lower course give off along their 

 whole track similar diverging fibres. So that, properly speaking, there are four main 

 pennate muscular bundles upon the surface, alternating with the course of the chymifer- 

 ous tubes, and four smaller ones following the tubes. With the arches rising from 

 these vertical bundles, an intimate connection is established by the more mesh-like 

 arrangement of the upper network of musculair fibres. In their course, all these fibres 

 remain chiefly superficial. Some of them, however, especially those of the four main 

 vertical bundles, penetrate more or less into the gelatinous mass, though they seem no- 

 where to meet the corresponding bundles, which, from the inner surface, penetrate like- 

 wise into the gelatinous disk, excepting, perhaps, in the lower portion of the disk near 

 its margin, where the gelatinous mass is much thinner, and where the superficial external 

 bundles seem to intermingle with the deeper bundles of the inner surface. 



The action of this muscular apparatus is quite obvious, both from the arrangement of 

 the bundles, and from direct observation. The upper network of fibres contracts the 

 upper part of the disk, while the vertical bundles shorten it, as they are strongest below, 

 and, when combined in action with the inner bundles, they turn the lower margin inward. 

 In this contraction, and especially when the vertical bundles are most shortened, the 

 four marginal buds are bent inward and brought nearer together. This is particularly 



