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Show 584 MR. E. A. MINCHIN ON THE ATTACHMENT [Nov. 19, capsules, such as are represented in figures 3, 4, and 5, the walls are relatively thick, containing a great deal of mesogloea, and the capsules themselves open by a comparatively wide opening into the lumen of the groove. In the larger capsules, on the other hand (figure 6), the mesogloea is scarcely visible, appearing as if squeezed out by the pressure of the numerous embryos contained in the capsules, and their openings are much narrowed. They always contain embryos in all stages of development, from segmenting ova to fully-formed planulse. In the series of sections from which figures 3, 4, and 5 were drawn, several ova were found of only four or eight segments. In addition to the embryos contained in the brood-capsules, a great number are always to be found free in the bottom of the groove or lodged in the foldings of its margin. M y excuse for publishing these details is that after I had made out the structure of the pouches from my sections, I consulted the numerous works on the anatomy and embryology of Aurelia, and found the brood-capsules quite erroneously described by Claus and Agassiz ; while in other writers I have found no mention of them at all. Claus (' Untersuchungen fiber die Organisation und Entwicklung der Medusen,' Prag, 1883) writes:-"The ova pass from the ovary into the gastric cavity and through the mouth between the apposed surfaces of the arms, where, surrounded hy a slimy excretory product of the endoderm (von einer schleimigen Absonderungs-masse des Entoderms umhullt), they run through their embryonic development up to the swarming planula, as if in a brood-cavity." I find this account to be incorrect, as far as m y specimens go. Agassiz (' Contributions to the Natural History of the United States,' vol. iv.) states (pp. 14 and 15) that the embryos of Aurelia flavidula leave the ovary as small ciliated larvse, either globular or oval in shape, and with distinct inner and outer walls1; in this condition they reach the pouches. In another passage (p. 58) he says : - " The ovaries .... discharge their eggs into the cavity above that floor [i. e. of the genital sacs], from which they have no other escape than through the channels leading into the main cavity of the body, from which they pass along the medial canals of the arms into the pouches formed by the foldings of their margin1, where they undergo their first development." In figure 9 of his plate viii. he represents some of the pouches containing " eggs and planulse." Speaking of Cyanea, he says:-"The eggs of Cyanea are able to lodge between the plications of the inner surface of the actinostome, though not provided with special pouches as in Aurelia." Thus Agassiz clearly recognized the fact that the embryos of Aurelia are carried in special pouches; but he wrongly describes their formation as foldings of the margin of the arm ; and, moreover, he states that the embryos do not reach them till they have attained the planula condition. If this is the case in Aurelia flavidula, it certainly is not so in A. aurita. I have succeeded in finding in the pouches embryos in all the stages described and figured by Claus 1 Tbe italics are not Agassiz's. |