| OCR Text |
Show 492 MR. E. T. BROWNE O N [Mar. 17 reproductive organs form a small oval swelling about halfwav down each of the four radial canals. In some of the specimens belonging to this stage the stomach is prolonged into the substance of the umbrella. The prolongation or apical stalk disappears in the later stages, but its presence indicates in some species that the medusa has not long been liberated from its hydroid. The mouth has four small lips. 2nd Stage. Eight tentacles.-The interradial tentacle-bulbs belonging to the first stage develop tentacles, and a few adradial tentacle-bulbs begin to appear. The marginal vesicles never exceed eight even in the adult form, but the otoliths show an increase in number. At this stage sometimes four otoliths may be present, but usually two or three. Width of the umbrella about 3 mm. and slightly less in height. 3rd Stage. Sixteen tentacles.-The adradial tentacles appear in no definite order, and when they reach nearly their full size other tentacle-bulbs commence to grow. The generative organs form a long oval patch upon tbe radial canals. The otoliths in each vesicle vary from two to four. Diameter of the umbrella 4 to 5 mm. Adult Form. (Plate X V I I . fig. 2.)-I place under this head all specimens with more than 16 tentacles. They increase in number until 32 is reached, but this number may not be the maximum, though it is the most I have seen in a specimen. The marginal vesicles always remain eight in nun ber, one of the characteristic features of the species and by which it m ay be distinguished from Phialidium temporarium. The otoliths in the vesicles show considerable variation even in the same individual. Three or four appear to be about the usual number present but sometimes more. One specimen had five to eight otoliths. Tbe umbrella becomes very thick especially at the aboral end. By the thickness of the umbrella I could usually recognize this species in an aquarium when in company with Phialidium temporarium. The generative cells, which in the earliest stage form a small oval patch about halfway down each radial canal, gradually grow downwards or outwards but do not touch the margin. Usually of a yellowish-brown colour. The largest specimen seen measured 13 m m . in width and4 mm. in height. During m y visit to Plymouth in September 1893 I saw several specimens of this medusa, belonging to the 1st and 2nd stages, and some early stages at Port Erin in M a y 1894. According to Haeckel this medusa, possessing only eight marginal vesicas and no cirri, ought to be placed in the genus Tiaropsis. But as the medusa is more like the species belonging to Phialidium than Tiaropsis, I prefer to place it temporarily in the genus Phialidium until its hydroid has been found, rather than make a new genus. EUTIMA INSIGNIS (Keferstein). Siphonorhynchus insignis, Keferstein (1862). |
