Chap. I. THE CORYNE MIRABILIS. 189 



long as the head (PI. XYII. Figs. 11 and 12), and at another contract to hardly 

 more than twice (PI. XIX. Fig. 1) or thrice their diameter (PI. XVII. Fig. 9, i*)- 

 In the latter condition they are strongly wrinkled, transversely. 



The whole community, including even the medusoe, when these are present, is 

 covered, from the base to the very tips of the tentacles, by a horny sheath (PI. XVII. 

 Figs. 9, c, 11, c, and 15, c, PI. XVIII. Fig. 8, and wood-cut G, i, p. (2.3), Fig. 10, and 

 wood-cut K, /, p. (24), Fig. 12, and wood-cut M, h, p. (24), Fig. 14, and wood-cut 

 N, h, p. (24), PI. XIX. Figs. 2, c, 3, c c\ and 4, c, PI. XX. Figs. 1, a, 2, c, 4, c, 5, c, 

 6, c c^). At the lower part of the branches, the sheath is quite thick, tough, and 

 like pai'chment in texture, but just below the heads it thins out, and becomes an 

 excessively delicate film, which yields to every flexure of the upper part of the 

 body and tentacles. It appears to be made up of irregular concentric layers (PI. 

 XX. Figs. 2, c, and 6, c). There are no traces of rings or twisting in this sheath, 

 as obtains in other species ; but it has a uniform surface, and the diameter of the 

 whole stem being about equal to that of a fine cambric needle (see PI. XVII. 

 Figs. 1 and 10), up to the base of the head, and thence expanding into the club- 

 shaped head, the sheath follow.s, also, over its surface and that of the tentacles. 

 Over the latter it becomes an exceedingly thin film, not to be easily observed 

 (PL XIX. Fig. 2, c). 



At the end of the season of the budding of the medusa^, in the sirring, a very 

 remarkable change takes place, not only in the head of the hydroids, but also in 

 the medusae. As late as the 26th of March, in 1855, the head of the hydroids 

 appeared perfectly normal in its characters, and the medusae, then l)udding (PI. 

 XVIII. Fig. 14), had every appearance of being fully developed in all their parts, 

 and about ready to drop from the pai'ent stem. Not three weeks later, April 

 13, 1855, so remarkable a change had come over the hydroids and the medusa 

 form, that, at first, the specimens then found were thought to be of a different 

 species from those studied in March. There was no appreciable difference to be 

 noticed in those hydroids which had the tentacles all perfect, but everywhere the 

 medusoid was unlike those found in the middle of the breeding season. Very few 

 hydroids had more than one medusoid adherent to them (PI. XVII. Figs. 10, 11, 12, 

 13, 14, and 15). In some instances the heads were perfect (PI. XVII. Figs. 11 and 

 12), in others the tentacles were shrunken, and looked more like prominent papillae 

 (PL XVII. Fig. 13), and again, the tentacles were all gone, and nearly the whole 

 head with them (PL XVII. Fig. 14), and finally, no trace of a head was to be 

 seen, but the stem was terminated by a medusoid with its mouth turned directly 

 upwards (PL XVII. Fig. 15). Still greater and more essential modifications were 

 found in the medusoids. All of them had an elongate, oval or ovate, form (PL 

 XVII. Figs. 11, 12, 13, 14, and IG), contrasting strongly with the globular contour 



