OCR Text |
Show 478 MR. E. T. BROWNE O N [Mar. 17, Agassiz (1865) has described a medusa, Lizzia grata (=Margellium gratum, Haeckel), which has five tentacles in each of the four perradial groups and three tentacles in each of the four interradial groups. From the specimens collected at Valencia, I have every reason for believing that Lizzia grata is the adult form of Margellium octopunctatum. The early stages of Margellium octopunctatum were fairly abundant in Valencia Harbour at the beginning of April, but decreased in number during May. Most of the specimens taken during April and the early part of May had one to four medusa-buds upon the stomach. About the middle of May specimens were taken with either ova or spermatozoa upon the wall of the stomach. The reproductive cells first begin to appear upon the perradial ridges on the outside wall of the stomach, and as they increase in size they form a mass covering the Mall of the stomach. As soon as the reproductive cells begin to appear, the budding of medusae ceases. The compound basal bulbs of the tentacles show little variation in colour, being usually dark brown or black. One specimen, however, had reddish-brown bulbs. The specimens taken at Valencia resemble those taken at Port Erin. I have no doubt that they belong to the same species, and as they were taken in a distant locality it may be of interest to record some for comparison with those taken at Port Erin. The following list shows the number of tentacles in each perradial and interradial group of 16 specimens taken at Valencia. It is also arranged to show the increase in the number of tentacles during the growth of the medusa. Perradial 3333 3333 3333 3333 3333 3334 Interradial 1112' 3231' 2222' 2333' 3333' 3333' Perradial 4343 5334 5344 5433 5444 4454 Interradial 3333' 3333' 3333' 3333' 3333' 3333' Perradial 5454 5553 5554 5555 Interradial 3333' 3333' 3333' 3333' The above series corresponds very closely with a series given in the Eeport on the Isle of M a n Medusae. Tbe umbrella of the earliest stage is about 1 m m . in length, and that of the adult from 3 to 4 m m. Not only does the medusa increase the number of its tentacles as it grows, but also the number of clusters of nematocysts upon the oral tentacles, which are four in number. Though some of the specimens taken off the Isle of M a n possessed the same number of tentacles as Margellium gratum, the clusters of nematocysts upon the oral tentacles were fewer in number. Until I had seen an exact similarity in every detail, I did not feel justified in placing Margellium gratum as the adult of Margellium octopunctatum. At Valencia I specially examined the oral tentacles of every specimen |