330 CONTRIBUTIONS TO THE NATURAL HISTORY 



Besides these main bundles of vertical fibres, we have as many more bundles alter- 

 nating with them, which arise from the upper end of the vertical rows of locomotive 

 fringes, and converge towards the margin of the mouth, combining their fibres more or 

 less with those of the alternating bundles, and forming in their combination the 

 powerful contractile apparatus which opens the mouth, and which, when this is shut, 

 appears like a regular area of fibres radiating in all directions, as seen in Fig. 5 and 11, 

 in which the mouth is absolutely shut, and contrasting most remarkably with that open- 

 ing when spread to the utmost, as in Fig. 10. Similar fibres, though less regularly star- 

 shaped, converge also from the lower extremity of the vertical rows of locomotive fringes 

 towards the anal area (Fig. 4), but, from the peculiar form of the latter, and the curve 

 of the chymiferous tubes around it, they have a somewhat peculiar arrangement. 



The circular or parallel fibres or bundles of muscles (Fig. 1, 2, and 4) extend 

 transversely from one row of the locomotive fringes to the other ; and although 

 transverse fibres pass under these rows, the circular muscular bundles cannot strictly 

 be said to extend in unbroken continuity all round the sphere, in parallel, hori- 

 zontal circles ; for the chief bundles extend only from one row of vertical fringes 

 to the next, their fibres being chiefly connected with the substance which gives at- 

 tachment to the locomotive combs, and the number of fibres stretching across beneath 

 being considerably reduced by the great development of the chymiferous tubes which 

 follow the locomotive rows. Again, there are along these tubes, and under the locomo- 

 tive combs, vertical fibres also, which interrupt the regular course of the circular ones, 

 though the vertical fibres are here less powerful and less numerous than in the middle 

 of the space between two locomotive rows, where the chief vertical bundles are accumu- 

 lated. Towards the upper or mouth end of the body, however, above the vertical rows 

 of locomotive fringes, the circular fibres seem to be circular all round the mouth (Fig. 

 10) ; or at least to form bundles which are crossed by the upper radiating muscular 

 fibres, and interwoven with them, but not broken up into distinct segments of circular 

 bundles. On the anal extremity of the body, the circular fibres are considerably re- 

 duced, though there are still some to be seen. 



Considered isolately, the muscular bundles cannot be compared to muscles, as they 

 exist in higher animals. They are, strictly speaking, isolated muscular fibres, loosely 

 scattered, but more or less crowded together throughout the gelatinous mass, or upon 

 some particular points of the body, and in particular directions presenting, when con- 

 tracted, so much of a cellular appearance, as to be easily compared with elongated 

 fusiform cells, assuming, indeed, frequently that appearance, and then passing again into 

 a thread-like form, sometimes regularly swollen in the centre, at other times more to- 



