OF THE HYDROMEDUS^E. 391 



Description of the Larva. In a previous paper (10, p. 19.j) I gave a brief account of 

 the hydra and young medusa, which I am now able to supplement with illustrations and 

 additional notes. Although I made many attempts to rear the young from the egg, I 

 succeeded only once, and the plannla is shown in PL 42, fig. 2. It is very opaque, and 

 as I obtained very few, I did not sacrifice any of them for examination, and learned very 

 little of the minute structure. In a living plannla it is easy to make out, at the posterior 

 end, an ectodermal invagination, which looks very much like the mouth of an invaginate 

 gastrula, but this resemblance is misleading, for the careful study of a similar structure 

 in the plannla of Eutima shows that the invagination has no connection with the diges- 

 tive cavity, but is an ectodermal gland for the attachment of the plannla. My few plan- 

 ulse of Turritopsis attached themselves in the angle at the bottom of the aquarium, where 

 examination was impossible, and 1 was not able to displace them without destroying 

 them. Finally, I broke the glass, and was fortunately able to secure, among the frag- 

 ments, one specimen which was uninjured, and this I have figured in PL 12, fig. 3. The 

 figure shows that the plannla does not become converted into a hydranth but forms a 

 root, a, from which the first hydranth, h, is formed as a bud. This has as yet no mouth 

 nor tentacles, but its oral end is enlarged and filled with lasso-cells. 



The only colony of the hydra which I obtained was scraped from the piles of the steam- 

 boat wharf at Morehead City, seven or eight feet below low tide mark. The tips of two 

 of its branches are shown at H, in PL 37. It lived for two weeks in the house, and set 

 free great numbers of hardy medusae which were reared until they had acquired the char- 

 acteristics of the genus. 



The upright steins of the hydra, from 8 mm. to 12 mm. high, bore large terminal hy- 

 dranths, as well as smaller ones which were scattered irregularly along the stem on short 

 stalks. The long fusiform body of the hydranth carries from eighteen to twenty thick, 

 short, filifi >rm tent acles, which are arranged in three or more indefinite whorls. The medusa- 

 buds, B, B, originate around the stem just below the hydranths, and t hey are themselves car- 

 ried on short stems. The perisarc is not annulated, audit formsa loose cylindrical sheath 

 around the main stem, and the short branches which carry the lateral hydranths and the 

 young medus;e, Avhile the latter are closely invested by a much thinner and more trans- 

 parent capsule of perisarc. The sheath on the stems is thick and crusted with foreign 

 matter. It terminates abruptly by a sharp collar just below each hydranth. The young 

 hydranths and the medusa' are budded off above the collar, but they soon become en- 

 tirely sheathed in perisarc by the growth of the stem. The pale yellowish-red hydranths, 

 are very similar to those of Tubularia (Allman) and the hydroid is so similar to Dendro- 

 clava Dohrnii recently described by "VVeisniann, that they undoubtedly belong in the 

 same genus. 



Metamorphosis of the Medusa. The little medusa remains attached to the stem, as 

 shown in PL 37, C, for some time after the rupture of its capsule of perisarc. At this 

 time it is nearly spherical and covered with large conspicuous ectoderm cells. Its eighl 

 short tentacles are thrown backwards in contact with the outer surface of the bell, and 

 their tips are hooked or bent upon themselves in a very characteristic manner, which is 



