OF THE ACALEPH^ OF NORTH AMERICA. 371 



Fig. H. An oblique view, partly profile, partly from tlic side of the mouth. The parts in sight correspond to Fig. 2, 

 only in an inverse position ; the tentacles moderately expanded. 



Fig. 12. A specimen moving downwards. The organs in sight correspond to Fig. 3, but in an inverse position ; the 

 tentacles slightly expanded, one of them coiled upon itself for some length, with a few fringes expanded. 



Plate 11. 



Fig. 1. Pleurobrachia rhododactyla in a vertical position, the main cavity and the digestive cavity in sight from its nar- 

 row surface, and the tentacular apparatus right and left. Fig. 5 gives a view, from the side of the mouth, of all parts 

 in the same respective position; and Fig. 4, another view from the opposite side, where tlie circumscribed area is seen 

 in the centre. 



Fig. 2 represents the same in profile, but in a position at right angles with that of Fig. 1 , so that the main cavity of 

 the body is .seen from its broad surface, and one of the two tentacular apparatus in the centre of the figure. To bring 

 Fig. 4 and 5 to agree in position with Fig. 2, they should be moved 90° upon their axes. 



Fig. 3 gives another profile view intermediate between that of Fig. 1 and that of Fig. 2 ; so that the two tentacular 

 apparatus are in sight, but in an oblique position forwards and backwards, and not right and left, as in Fig. 1, or in the 

 centre, as in Fig. 2. 



Fig. 4, 5. To bring Fig. 4 and 5 into the same position, they should be turned 45° upon their axes. 



Fig. 6. A part of one of the vertical rows of locomotive combs, behind which is seen the vertical chymiferous tube, 

 into which opens one of the horizontal radiating tubes. 



Fig. 7. A portion of one of the vertical chymiferous tubes, the fringes of the locomotive combs being removed to show 

 the bases of the latter, and the ganglia behind them. 



Fig. 8 represents half the width of a vertical chymiferous tube, with muscular fibres behind it, and the granules cir- 

 culating in its cavity. 



Fig. 9 represents a portion of a vertical chymiferous tube similar to that of Fig. 7 ; but the tube is more contracted, 

 and its walls so folded longitudinally as to present distinctly several parallel waving lines, which have no existence in 

 reality when the tubes are fully expanded, but appear only when the tubes are separated from the body, and empty. The 

 same lines appear also in Fig. 7. 



Fig. 10. The mouth widely open, with the muscles which open and slxut it around. 



Fig. 11. The mouth when fully shut. 



PL.4TE III. 



Various figures to show tlie course of the chymiferous tubes, the relations between the alimentary cavity and the 

 main cavity of the body, and the connection of the tentacular apparatus with the chymiferous tubes. To render the fig- 

 ures more distinct, the fringes of the vertical rows of the locomotive combs have been omitted. The chymiferous tubes 

 and the main cavity of the body are shaded. In Fig. 6 and 7, however, the shaded parts represent the digestive cavity. 



Fig. 1. Corresponding in position to Fig. 2 of Plate II., and showing the connection of the four vertical chymiferous 

 tubes of one side with the main horizontal chymiferous tube, the vertical funnel, the tentacular apparatus, and the vertical 

 chymiferous digestive cavity. 



Fig. 2. Corresponding in position to Fig. 1 of Plate II., and therefore placed in a position at right angles with that of 

 Fig. 1, to show the relations of the chymiferous tubes and the main cavity in that position. 



Fig. 3. The same parts seen from the side of the circumscribed area. 



Fig. 4. The same parts seen from the side of the mouth. 



Fig. 5. The tentacular apparatus in its cavity, to show the origin of the tentacle and the connection of the vertical 

 chymiferous tubes of the tentacle with the main horizontal tube, and its branching forks. 



Fig. 6. The digestive cavity entirely empty, and flattened in the position of Fig. 2. 



Fig. 7. The same cavity, more expanded. In c, the brown cells at the lower extremity of the cavity give its surface 

 a peculiar appearance. 



