OF THE ACALEPH/E OF NORTH AMERICA. 329 



arisiii;^ at right angles with the vertical row, and extending sideways; at times diverging 

 in four directions, as in Fig. 7 ; and at times the two kinds of fibres, though less roo-ular, 

 would appear in connection with them, as in Fig. 9. Whether these swellings, and the 

 threads arising from them, arc sensitive ganglia, sending out nervous threads, or whether 

 their appearance, which is subject to so many irregularities, is the result of the con- 

 traction, and perhaps of the commencing decomposition, of numerous muscular fibres, 

 lining the inner surface of the vertical rows of locomotive fringes, must remain doubtful. 

 I should say, however, that I have never been able to discover these parts in the living 

 animal, though they are readily found upon slices cut from it, often immediately after 

 their removal. The appearance I noticed in the surface of the body between the combs, 

 when kept apart, was always similar to what is represented in Fig. 8, where muscular 

 fibres crossing each other in various directions were chiefly visible; and, below, were 

 granules floating through the chymiferous tube, accumulating generally to a great amount 

 in the centre (a), — owing, no doubt, to the greater diameter of the tube when seen in 

 such a position, — and apparently fewer towards its margin (6), where the oudine appears 

 as a double line. But the great transparency of ail these parts makes it exceedingly 

 difficult to arrive at any precise conclusion, even with regard to their respective position. 



^Vith the spherical form characteristic of the family of Beroe, the general arrange- 

 ment of the muscular bundles is also somewhat modified, though regulated by the same 

 principle which prevails in the arrangement of the muscles in the Discoid Medusae. 

 Here, also, we have vertical bundles and circular ones, but, owing to the spherical form 

 of the body, these extend all round the sphere from one pole to the other, like the 

 meridians and parallels of an artificial globe, modified in the details of their arrange- 

 ment by the form and extent of the mouth, by the disposition of the area opposite to it, 

 and by the width and extent of the vertical rows of locomotive fringes, and also by 

 the presence and position of a special cavity for the tentacles. 



In Pleurobrachia proper, the vertical rows of muscular fibres are eight in number, 

 alternating with the rows of locomotive fringes, beginning about the same height as 

 those on the mouth side of the body, as is seen in Fig. 1,2, 3, and 5, and extending 

 to about the same distance from the opposite centre, where their arrangement, however, 

 is considerably modified by the peculiar form of the circumscribed area of the anal end 

 of the l)ody. Six of these vertical bundles are nearly identical in their arrangement, 

 but the two lateral bundles (Fig. 2), which extend in the direction of the axis of the 

 tentacles, are somewhat modified by the opening from which the tentacles arc issued, 

 their fibres diverging and converging again, so as to have a direct influence upon the 

 cavity in which the tentacles are contained. 



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