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Show 1896.] BRITISH HYDROIDS AND MEDUS.E. 479 taken, aud found a few specimens agreeing with Agassiz's description of Margellium gratum, both in the number of marginal tentacles, and in the number of clusters of nematocysts on the oral tentacles. I think this removes all doubt concerning the identity of the two species. In the Valencia specimens the clusters of nematocysts develop in the following order :-The earliest stage has each oral tentacle terminating in a single cluster of nematocysts. A second cluster appears near the first cluster upon a short stalk; the tentacle then appears bifurcated, each branch terminating in a round cluster of nematocysts. Two more clusters, each on a short stalk, make their appearance, one on each side of the tentacle, about the middle of its length. This was usually the appearance of the oral tentacles in all the large specimens taken at Port Erin and at Plymouth. At Valencia, in a few of the largest specimens, with four or five tentacles in each perradial group, I observed on each oral tentacle a second pair of lateral clusters of nematocysts, below the first pair. One specimen had a fifth cluster on a short stalk situated midway between the two terminal clusters. This agrees with the development of the clusters described by Agassiz in Margellium gratum. Another specimen, however, showed a variation in development, by possessing three terminal clusters and only a single pair of lateral clusters. Allman (1859) has described and figured a Calyptoblastic hydroid, Laomeclea tenuis [ = Leptoscgphus tenuis, Hincks (1868)], wdiich he found at Stromness. The hydroid has gonothecae each containing a medusa. AUman has not given any description of the medusa inside the gonotheca, and from the figure it is impossible to identify it, chiefly on account of its being at a very early stage in development. Allman found inside the jar containing this hydroid a number of young medusae which he believed to be closely related to the genus Lizzia. From the description given of these medusae I believe they are probably an early stage of Margellium octopunctatum. Allman regards these free-swimming medusae as the medusa of the hydroid in the jar. This observation has never been confirmed, and if it be true, then a case is estabhshed in which a Calyptoblastic hydroid produces Anthomedusae. Allman does not state that he has seen a single medusa leave the hydroid nor show in any way that the medusa inside the gonotheca resembles the free-swimming Lizzia. I do not think that there is sufficient evidence to prove that the medusae came from the hydroid, and I hesitate to accept the statement until the observations have been confirmed. It is quite possible that the young Lizzia entered the jar along with the sea-water. DISTRIBUTION. America-Massachusetts Bay, Agassiz. Norway, Sars. France-Wimereux, Giard. Scotland-Shetland Islands, Forbes. St. Andrews, M'Intosh. England-Plymouth, Garstang; Allen. Fowey, Peach, Palmouth, Vallentin. Isle of M a n , Browne. Ireland-Valencia Island, E. T. B. |
