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Show 1°89.J OF THE EMBRYOS IN AURELIA. 585 (loc. cit.), from segmenting ova to the fully formed planulse or "clistogastrulse." Other Medusae belonging to the Acraspeda carry their ova about during the first stages of development. Von Lendenfeld states (Proc. Linn. Soc. N. S. Wales, vol. ix.) that in Pseudorhiza " the embryos are carried about in pouches suspended in great number from the radial canals which run centripetally from the ring-canal. They remain there till they are fit to turn into young Scyphistomes." In Stylorhiza (Phyllorhiza) punctata, he says (loc. cit.), "the young embryos adhere to the mother's filaments until they have nearly attained the Scyphistoma stage." The same author describes ('Zeitschrift fiir wiss. Zoologie,' 1888, p. 301) in Cyanea anaskala and Phyllorhiza punctata a peculiar arrangement of filaments on the underside of the arms, by which the embryos appear to be nourished. P.S., Dec. 9, 1889.-Since writing this article my attention has been directed to Ehrenberg's paper, "Ueber die Akalephen des rothen Meeres und den Organismus der Medusen der Ostsee" (Phys. Abhandl. Akad. Berlin, 1835). Ehrenberg gives a rough figure of Aurelia aurita showing a magnified external view of the pouches and their contained embryos (Taf. viii. fig. 1, and Taf. iii. fig. 1) ; and states (p. 197), first, that the brood-pouches are either formed by the pressure of the " Kugeln " (i. e. ova and embryos) which collect in the groove of the arms, or else are preformed by the mother for their reception ; secondly, that the pouches increase in size as more embryos crowd in ; and thirdly, that when the embryos quit the pouches the latter collapse and disappear. EXPLANATION OF PLATES LVII. & LVIII. In all tbe figures ect denotes tbe ectoderm ; mes, the mesogloea; end, tbe endoderm ; d, digitellas; and tbe letter G* is placed in tbe lumen of tbe groove of tbe arms. Fig. 1. .An oral arm of Aurelia aurita, covered with tbe little pouches containing embryos. The letter m is placed in the cavity of the mouth. 2. A transverse section of an oral arm which was entirely without brood-poucbes. The numerous plications are due to the arm having been crumpled while preserved in spirit. 3. A transverse section of an arm which had few and somewhat small pouches, a and b, two of the pouches containing embryos. 4 & 5. T w o more sections through the pouches lettered a and b in the last figure. 6. A transverse section through an arm which had numerous and very large brood-pouches. Only one side of the section is drawn, c, d, e, and /, four pouches, each containing a great number of embryos, those in c, d, and/being only represented in outline. P R O C ZOOL. Soc-1889, No. XXXIX. 39 |
