OF THE ACALEPH^ OF NORTH AMERICA. 277 



the case when the lower parts of tlie vertical bundles of the inner and outer surface of 

 the gelatinous disk act simultaneously ; but when the outer ones alone are contracted, 

 and especially the small bundles (Plate III. Fig. 2, e, e, e) above the buds are in activity, 

 they expand the sphere again, and turn the buds outward and upward. 



Though, perhaps, less complicated in their course, the inner vertical muscular bundles 

 (Plate III. Fig. 3, 4, 7, 8, 9, d, d, e, c, f, f) which line the inner surface of the gelati- 

 nous disk are still more difficult to trace, and their action is less easily ascertained. There 

 are four main bundles (f?, d), the position of which is easily recognized. They arise 

 from the lower surface of the gelatinous disk, above the digestive cavity, between the 

 radiating tubes (Plate III. Fig. 9), and follow a vertical course, their fibres remaining 

 closer together than those of the external layer ; though here, also, the contractile cells 

 diverge upwards and downwards in such a manner as to give each of the bundles some- 

 what the appearance of a pennate muscle. These bundles (Plate III. Fig. 3, 4, rf, d) 

 terminate below the margin midway between the sensitive buds. Their fibres penetrate 

 more deeply into the gelatinous mass, especially below, where they meet the superficial 

 bundles, and intermingle with them (Plate III. Fig. 8, d, a, d, a, d, a), under acute 

 angles, a being the superficial, and d the inner vertical bundles. Of course, seen in 

 profile (Fig. 3, 4), these bundles follow the curve of the gelatinous disk, which is the 

 same as that so plainly shown by the chymiferous tubes. When seen from above (Fig. 

 7, 9), it might easily appear as if there were several bundles of muscles placed one above 

 the other ; for in this position, the arch which the bundle forms from the centre towards 

 the lower margin is so foreshortened, that its upper portion is seen separately from the 

 lateral portion ; and as this is straighter, the appearance is as if a stronger muscle were 

 placed outside of the feebler one, which seems to be nearer the digestive cavity. But a 

 vertical view (Fig. 3, 4) will leave no doubt about the continuity of these muscles, 

 and easily show that the appearance noticed from above is that which a vertical pen- 

 nate arch would present if it were drawn so that both the arched and the vertical 

 part could be seen projected upon the same plane (Fig. 7, d). Then the arched part 

 passing into the vertical stem would be foreshortened so as to appear very thin, and the 

 long vertical branch itself would appear very strong, from the many branching fibres 

 thus accumulated upon each other in the vertical view. In Fig. 7, f/, where these 

 main bundles are thus foreshortened, they appear like anchors, owing to the particular 

 focus under which they were drawn ; when, in addition to the complications already 

 mentioned, the pennate arrangement of the fibres appeared most prominent, and formed, 

 as it were, the two curved arms of the anchor. 



Alternating with these main bundles, there are eight others (Plate III. Fig. 3, 4, 7, 



38 



