Report of the Meetings Volume 20

Report of the Meetings Volume 20

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1851 edition. Excerpt: ... overlapping each disc. The ova in the different species vary from a lenticular shape to an elongated oval, and in Fredericella the marginal ring is obsolete. In all, one surface would eem to be a little more convex than the other. In C-ristatella the mature ovum is furnished with hooked spines, which spring alternately from the two sides just within the annulus, and thence passing outwards over the latter project in short rays beyond the margin. The disc in all the species is of a deep brown colour, and would seem to be composed of a single layer of hexagonal cellules, whose external walls in most cases slightly project beyond the surface of the disc, and thus give to the latter an elegantly mammillated condition. In some cases however the cellular condition of one or both discs is very obscure. The annulus is also composed of cellules, which here, however, occur in several layers; these cellules are also for the most part larger than those of the disc and of a different colour; they are filled with air, and give to the annulus a light spongy texture. In C1-istatella I have succeeded in tracing certain stages in the progress of the ovum towards the mature condition, in which it is ready to escape from the body of the parent. In an early stage it may be observed as a whitish semitransparent compressible vesicle enclosing a fluid loaded with granules or minute cellules. In this state its surface is perfectly smooth, but we find it before long acquiring two additional investments, which however possess but a temporary existence and are destined to disappear as the ovum advances to maturity. The internal of these is a thick layer of a gelatinous consistence, which immediately invests the ovum; the external is a delicate transparent membrane...show more

Product details

  • Paperback | 342 pages
  • 189 x 246 x 18mm | 612g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236883330
  • 9781236883339