Chap. V. THE GENUS POLYCLONIA. 141 



When brought into large glass jars, in a swimming attitude, they assume, alter- 

 nately, two vei-y different positions. When at rest (PI. XIIP. Fig. 1) and floating, 

 the umbrella is slightly and uniformly arched downward, the margin alone expand- 

 ing and contracting gently, while the peduncle, with its eight arms, hangs loosely 

 down, the ramifications of the arms being turned inward, and slightly folded together. 

 In this condition the actinostome projects so far below the umljrella, that the holes, 

 leading into the genital pouches, are easily seen. When more active (PI. XIII.), 

 the actinostome is drawn up and spread under the mnbrella, in such a manner, 

 that all the ramifications of the arms are turned outside, and present the appear- 

 ance of innumerable ramifications interlocked with one another. The disk is alter- 

 nately expanded and contracted, so as to assume, in its contracted condition, an 

 hemispherical form, while in the expanded condition, PI. XIII. Fig. 1, the centre 

 of the umbrella is alone raised above the level of the peripheric part of the disk, 

 and the margin hangs abruptly down. PI. XIIP. Fig. 6, represents this species 

 from above, part of the outline being suppressed; PL XIII. Fig. 2, represents it 

 from below; but, to avoid a useless multiplication of the figures, different parts 

 are drawn in different segments, or the same parts in a different state of preser- 

 vation, or in a different state of contraction, and one segment, 7, is represented 

 as injected. In segments I and 2, two arms are drawn in their natural expanded 

 condition, showing their junction near the centre, and the peculiar appendages 

 Avhich cover the surfece of the centre, in the females. In segments 4 and 5, 

 two other arms are represented without the delicate fringes of their margin, in 

 order to show how the edges of the arms are soldered in Rhizostomeae. This 

 mode of connection extends to the very centre of the lower floor, even to the 

 part covered by the peculiar appendages of the centre. In segments 7 and 8, 

 near the centre, these appendages are represented as they appear in the males, m. 

 Outside of these appendages, in segments 7 and 6, the chymiferous tubes are injected, 

 in order to show their ramifications and anastomoses. In segments 8, 9, 10, 11^ 

 and 12, the surface of the lower floor is exhibited in a natural condition, but in 

 different states of expansion and contraction. When most contracted, as in seg- 

 ment 8, it is marked by undulating furrows, following mainly the direction of the 

 principal branches of the chymiferous tubes; in a less contracted condition, as in 

 segments 9 and 10, the wrinkles are more numerous, but less deep, and do not so 

 distinctly exhibit their relation to the chymiferous tubes, near the margin, though 

 it is quite apparent nearer the central cavity. In segments 11 and 12, the lower 

 floor is entirely stretched, and appears smooth. Notwithstanding the changing aspect 

 of the lower floor, the folds described above are imquestionably determined by 

 structural relations, and it is a significant fact, that their general disposition recalls, 

 in the most striking manner, the ramifications of the ambulacral furrows, npon the 



