﻿OF THE ACXLEPHJE OF NORTH AMERICA. 237 



though far apart ; as they generally follow the modifications of the main bundles, some- 

 times arising almost from the same point, and at other times more apart, but evidently 

 always lending their influence, in their contraction, to the action of these bundles. 

 Seen from below (Plate V. Fig. 4), the whole system appears rather like a brush of 

 muscular bundles diverging downwards, then slightly converging to meet the lower 

 margin without uniting again, and forming there twelve bundles, four of which are 

 stronger than the other eight. By this arrangement, the bundles appear more or less 

 pennate as they converge or diverge. I may say, that this whole system of superficial 

 muscles is never seen, but by its action, unless the specimens are dead, and have been dead 

 for some time, when, during the contraction which follows death, they are made tem- 

 porarily visible, and can then be traced with certainty in all the details of their arrange- 

 ment, under the microscope. In Fig. 3, Plate V., small transverse superficial bundles are 

 seen, connecting the secondary vertical bundles. In the two figures of Plate V., above 

 cited, the inner muscular systems, and the digestive and chymiferous apparatus, have 

 been drawn in outline, in connection with the more complete and finished delineation of 

 the system of external muscles, in order to allow a comparison with Fig. 1 and 2, 

 where the inner muscular systems have been drawn with particular care, and the outer 

 omitted. The possibility of thus separating the investigation of these two systems, 

 which otherwise cover each other so closely, will satisfy every one of the necessity of 

 close investigation of these parts to understand them well. When highly contracted, 

 they seem to run together. (Plate V. Fig. 6, d, d.) 



The inner system (Plate V. Fig. 1, 2, 11) follows closely the same arrangement, both 

 in the direction of the fibres, running vertically from the upper centre downwards, and 

 in their mode of diverging and converging, by which they form similar pennate bundles ; 

 except that here the central bundles d, d, d, d, are more prominent than the two accessory 

 ones, e,e,e,e, f,f,f,f, which follow them. Though these bundles are chiefly superficial 

 on the inner surface of the gelatinous mass, they penetrate more or less into the gelatinous 

 body, and their arrangement is so peculiar, that it cannot be compared with the arrange- 

 ment of muscular fibres in any other group of animals. As described above, the gelatinous 

 mass of the body is bell-shaped, thickest in its upper arched part, thinnest below, where the 

 margin is bent inwards at right angles ; and this whole mass is very elastic. Now the 

 muscular bundles can neither be said to rest simply upon the inner or outer surface of this 

 body, nor to rise within. There are bundles which lie outside or near the outer surface, and 

 others which lie within the gelatinous mass, and others, again, which rise more or less ob- 

 liquely from within, and extend towards the surface ; so that the muscular bundles arc 

 properly loose bundles, the fibres of which penetrate unequally into the gelatinous mass ; 



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