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PROCEEDINGS OF THE 



[Jan., 1856. 



however, folds and plications of the surface are formed in the 

 muscular areas which indicate at least the presence of contractile 

 cells acting in regular lines. These are represented in PL 7, fig. 

 87. Two sets of plications in different directions were observed 

 at different times, one probably representing circular fibres stretch- 

 ing transversely across the muscular lobes, but bending outwards, 

 to some extent following the convex outline of the lobe. It 

 will be observed also, PL 7, fig. 34, x, that between the prolonga- 

 tions of the digestive cavity and stretching from one tentacular 

 bulb to another is a delicate thread. This consists of somewhat 

 elongated oval cells (fig. 42,) differing in appearance from those 

 about them, and which I have not observed to contract. Possibly 

 they may be the rudiment of a nervous circle around the stomach. 

 On each side of this thread and radiately with respect to the cen- 

 tral axis of the animal, can be observed plications resulting from 

 contraction, which have a direction corresponding to that of the 

 longitudinal fibres described by Agassiz in Sarsia. These are all 

 the indications of muscular tissue. The walls of the digestive 

 cavity are formed by a tissue of circular cells which are larger and 

 more densely crowded at the junction of the upper and lower wall. 

 A thickening of the lower wall of this cavity forms the border of 

 this simple mouth, and is coloured yellow, being the only coloured 

 part of the larva. The vail is composed of larger and sometimes 

 slightly elongated cells of a different aspect, they are arranged 

 so as sometimes to present an appearance of obscure rows trans- 

 verse to the diameter of the vail, and are undoubtedly contractile 

 (Fig. 34, v.) These peculiar cells of the vail, but with less regular 

 juxta-position, characterise the prolongations of that membrane 

 between the muscuJar lobes, up to the bases of the tentacula. 

 (Fig. 35, a.) The thickened cord or border of the lobes appears 

 to pass into the bulb of the tentaculum as in Thaumantias, forming 

 that outer sheath which when viewed by transmitted light, presents 

 the appearance of two thickened crura. From this bulb projects 

 inwardly into the thickened border of the stomach a prolongation 

 of the large cell structure forming the core of the tentaculum. It 

 is represented fig. 36, e. The form of the terminal club-like en- 

 largement of the tentacle is represented PL 5, fig. 29. That this 

 bulb does actually and forcibly attach itself is shown in fig. 30, 

 PL 6, where a portion of the inner surface of the parent is pulled 

 up, after the tentacular bulbs which tenaciously maintain their 

 hold, even when the larva has been forced somewhat away from 



