Text-Book of the Embryology of Invertebrates

Text-Book of the Embryology of Invertebrates

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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. 1899 edition. Excerpt: ...of cells lying somewhat behind the stomodaeal invagination; this mass of cells gives rise to three pairs of hepatic tubes. At a later stage, a layer of cells connected with the epithelium of the hepatic tubes grows over the whole of the food-yolk. The rudiment of the mid-gut now consists of the yolk-vesicle thus formed and the hepatic tubes communicating with it. The anterior end of the yolk-vesicle is connected with the stomodaeal invagination. The proctodaeal invagination, on the contrary, is not in contact with the posterior end of the yolk-sac, but runs forward over its dorsal side so as to pass into it quite near the stomodaeal invagination. The yolk-vesicle appears now as a ventral diverticulum of the alimentary canal, but, as most of it undergoes absorption, it results that here also only quite a small part of the definitive intestinal canal near the points of entrance of the hepatic tubes belongs to the mid-gut (cf. p. 139 on Ligia). The above description of the formation of the mid-gut in the Arthrostraca, founded on the observations of Bullar, Nukbaum, Pereyaslawzewa, and Rossijskaya, applies, according to Nusbaum, to Mysis also (Figs. 65 and 66, p. 135). The entoderm here originally lies as a mass of cells in the most posterior section of the germ-band (p. 134). The entoderm-cells soon increase in number, and spread out over the whole ventral surface of the embryo. At a later stage they also reach the lateral and dorsal parts, the food-yolk in this way becoming surrounded by a layer of entoderm-cells While this circumcrescence is going on in the posterior part of the embryo, the entoderm in the anterior part (behind the mandibular segment) forms two lateral grooves consisting of large granular cells (Fig. 66, I); these are the...show more

Product details

  • Paperback
  • 189 x 246 x 8mm | 272g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 123689698X
  • 9781236896988