Chap. III. HISTOLOGY OF CYANEA. 113 



and upon their contraction transverse wrinkles appear between them. The outer 

 surface of the actinostome exhibits mainly epithelial cells, of a very uniform ap- 

 pearance, between which are scattered a few lasso-cells; but on the inner surface of 

 the whole actinostome a different arrangement prevails, there being innumerable 

 clusters of lasso-cells scattered over the whole of that surface, and especially crowded 

 towards the margin of the lobes (PI. IV. Fi(j. 4). Fig. A, a, represents such a 

 cluster, magnified 250 times in diameter. The form of these lasso-cells is peculiar ; 

 they are more globular than is generally the case among Acalephs, and, in that 

 respect, resemble the lasso-cells of Physalia very closely, and when the coil is everted, 

 the neck, which connects the thread with the bag in which it was coiled up, is 

 smooth, and entirely destitute of those hook-like jirojections which are character- 

 istic of the lasso-cells of the Hydroids. The whole margin of the lobes or fringes 

 of the actinostome is entirely occupied by a narrow seam of smaller lasso-cells, as 

 seen in PI. V. Fig. 3, which represents a band along the inner surface of one of 

 these lobes, extending from its margin towards the interior, wp to a distance, where 

 the clusters of lasso-cells are less crowded. Following, in the same direction, the 

 arrangement of these cells upon that surface, it is seen, that above the narrow 

 band which is entirely occupied by lasso-cells, the epithelial cells intervening 

 between the clusters of lasso-cells are smallest, and become gradually larger higher 

 up, until, increasing in size, in proportion as the clusters of lasso-cells are fewer, 

 they have become singly, almost as large as a cluster of lasso-cells. Fig. 3, d, 

 represents the small lasso-cells of the margin, more highlj^ magnified ; Fig. 3, c, 

 represents a portion of the surface immediately above, where the epithelial cells 

 are smallest; Fig. 3, b, a space higher ujj, where larger lasso-cells intervene between 

 the smaller ones, and Fig. 3, a, a space higher up, where the larger epithelial cells 

 cover the whole surface, with a few scattered small ones between. This arrangement, 

 and the prevalence of clusters of lasso-cells on the inner surface, is probably intended 

 to facilitate the introduction of the food along the complicated system of folds of 

 the actinostome up to the oral aperture, and probably, also, to retain the eggs 

 between these folds, at the time of spawning, and to prevent them from dropping 

 into the water, at a time when the embryos are not yet so far developed as to 

 be capable of swimming freely about, befoi-e attaching themselves to the surfaces 

 upon which they undergo their further development. 



The tentacles present a still greater diversity, both in the arrangement and in 

 the appearance of their cells. The hollow channel which traverses the tentacles, 

 for their whole length, is uniformly lined with exceedingly minute epithelial cells, 

 as represented in PI. V. Figs. 11 and 12. These cells vary in color, being yellow, 

 orange, purple, or brown, in different tentacles, and they chiefly determine the color 

 of these organs, for the walls of the tube consist of a transparent gelatinous mass, 



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