OCR Text |
Show 824 MR. E. T. BROWNE ON BRITISH MEDUSA. [Nov. 16, Some of the other synonyms refer to medusae which do not belong to the genus Laodice, but two of them clearly do, viz., Thaumantias mediterranea, Gegenbaur (1856), and Cosmetria punctata, Haeckel (1864). Haeckel, however, in his monograph (1879), rightly considers that his species is identical wdth that of Gegenbaur, and therefore may be regarded as a synonym of it. It is a matter of considerable difficulty with our present knowledge of the genus to fix upon characters which may be regarded as sufficiently permanent to distinguish one form from another. Although I obtained last year several dozen fine specimeus in Valencia Harbour, yet I am not able to determine for a certainty to which species they belong. I first used the specific name L. calcarata for a specimen taken off the Isle of M a n in 1894, and at that time had not investigated the literature connected with Laodice cruciata of Haeckel. As I do not wish to change again the specific name of the British specimens the name is still retained for the Irish specimens, which would fairly well agree with any of the four species mentioned, except in coloration, which, amongst medusa?, is not usually a good character for the determination of species. Tbe Valencia specimens ranged from 3 m m . to 27 m m . in diameter and show various stages in development. The umbrella is changeable in shape, and cannot be relied upon as a specific character. In the smallest specimen the umbrella is bell-shaped, about as long as broad, but it broadens as it grows, as the following measurements show:-9 mm. wide, 7 m m . long; 20 m m . wide, 12 m m . long ; 25 m m . wide, 13 m m . long. Amongst the larger specimens, 20-25 m m . in width, the shape of the umbrella is very variable, from bowl-shaped to watchglass-shaped. The velum increases in width along with the growth of the umbrella, measuring 2-2| m m . in specimens from 20-25 m m . in diameter. The mouth in the smallest specimen has four lips with a slightly folded margin. The size of the lips and the folds of the margin increase with the size of the medusa. In the largest specimeus the lips are 2-4 m m . in length aud have a beautifully folded margin. The mouth opens direct into a flat stomach, out of which run the four radial canals. The generative cells develop in the wall of the radial canals, and the ova in the adult are visible, extending nearly from tbe stomach to within a short distance of the ring-canal. The smallest specimen (3 m m . in diameter) just shows the commencement of the formation of the gonads, by an increase in the size of the wall of the canals, forming a short fold which extends from the stomach and just arches over the top of the umbrella-cavity. It gives to the stomach the appearance of possessing four short lobes. The growth of the gonad continues along the radial canal until it nearly reaches the ring-canal. As the generative cells increase in size, the wall of the canal also increases in size, until it forms a large hollow tube with crumpled sides. In each of the specimens examined there was a short portion of the radial canal, next the ring-canal, free |