Chap. V. THE GENUS POLYCLONIA. 145 



tion of au arm of Aurelia, shows the same marginal tentacles {b b) along its edge, 

 as we have in Polyclonia (PI. XIII. Figs. 15 and 16, t t), and the narrow openings 

 [s s), leading into their channels, correspond to the fissure which extends between the 

 same tentacles in Aurelia (PI. VII. Fig. 7), and leads, also, into the main channel 

 («) of the arm. If we can speak of a mouth among Eadiates, it i.s, therefore, 

 the whole extent of the margin of the In-anching arms which forms its outline, 

 exactly as in Aurelia, PI. VI. Fig. 3. But for a mouth so constructed, a distinct 

 name was needed, and as that structure is homologous throughout the type of 

 Radiates, I have called it actinostome. The actinostome of Polyclonia has only 

 this peculiarity, that near the base of the arms, where their margins are entirely 

 soldered together, there are no apertures at all leading into the main cavity, and 

 yet, even here, the sutures of these margins may be noticed as shallow furrows 

 along the middle of the main branches of the arms (PL XIIP. Fig. 5, s s), while 

 at their extremities (t? J) the terminal marginal lobules conceal these furrows, as 

 well as the pores, or fissures, scattered along their course (PI. XIII. Figs. 15 and 

 16, s s). Besides the mere fissures, indicating the points at which the margins 

 of the arms are not soldered together, there are specialized pores, or small rounded 

 apertures, scattered, at greater intervals, along the soldered margins of the arms, 

 Fig. 2, well seen upon the arms of segments 4 and 5, in which the marginal lobules 

 are removed. Two such pores are particularly noticeable, about the centre of the 

 lower floor, Fig. 2, in a position which is homological to the extremities of the 

 straight line formed by the closing of the margins of the arm, across the mouth, 

 in Aurelia, PI. VI. Fig. 1. The outer surface of the arms is rounded aud smooth 

 (PI. XIIP. Figs. 1 and 4). 



In the centre of the lower floor, between the connected base of the arms, hang 

 peculiar appendages, consisting of a variety of papillte, or lasso-tentacles, of a most 

 diversified size and form. They are thinnei-, larger, and more pointed [Fig. 11) 

 upon the ramifications of the arms, and more club-shaped {Fig. 10) upon the centre 

 of the actinostome ; here and there there are large ones, paddle or shovel-shaped, or 

 cylindrical, with one or several patches of lasso-cells, either on one side only or 

 on both sides [Figs. 8 and 9) of the jjapillaj. The lasso-patches are white, with 

 yellow specks; the stems of the lasso-tentacles are greenish, and their lobes yellow, 

 and the tentacles themselves white. The microscopic structure of these singular 

 appendages is very peculiar; the yellow patches consist of clusters of strongly pig- 

 mented cells (PI. XIII. Fig. 12, g); the position of these patches upon the tentacles 

 may be seen in Fig. 14, g g. The shovel-shaped tentacles with lasso-patches {Fig. 

 13) have a similar structure as .the preceding, but on opposite sides there are com- 

 paratively broad patches of lasso-cells, closely jiacked together, and varying somewhat 

 in size and structure (PI. XIII. Fig. 17, a b c d c); when uncoiled, these cells exhibit 



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