Principles of Zoology; Touching the Structure, Development, Distribution and Natural Arrangement of the Races of Animals, Living and Extinct; With Numerous Illustrations. for the Use of Schools and Colleges. PT. I. Comparative Volume 1

Principles of Zoology; Touching the Structure, Development, Distribution and Natural Arrangement of the Races of Animals, Living and Extinct; With Numerous Illustrations. for the Use of Schools and Colleges. PT. I. Comparative Volume 1

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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. 1848 edition. Excerpt: ... multiplication by means of buds, and fissiparous reproduction, or propagation by division; and also some still more extraordinary modifications yet involved in much obscurity. 329. Reproduction by buds occurs among the polyps and some of the infusoria. On the stalk, or even on the body of the Hydra, and of many Infusoria (Fig. 132), there are" formed buds, like those of plants. On close examination they are found to contain young animals, at first very imperfectly formed, and communicating at the base with the parent body, from which they derive their nourishment. By degrees the Fig. 132. animal is developed; in most cases, the tube by which it is attached to the parent withers away, the animal is detached and becomes independent. Others remain through life attached to the parent stalk, and in this respect, present a more striking analogy to the buds of plants. But in the polyps, as in trees, budding is only an accessary mode of reproduction, which presupposes a trunk already existing, originally the product of ovulation. 330. Reproduction by division, or fissiparous reproduction, is still more extraordinary; it takes place only in polyps and some infusoria. A cleft or fission at some part of the body takes place, very slight at first, but constantly increasing in depth, so as to become a deep furrow, in the same way as takes place in the yolk, at the beginning of embryonic development; at the same time the organs are divided and become double, and thus two individuals are formed of one, so similar to each other that it is impossible to say which is the parent and which the offspring. The division takes place sometimes vertically, as for example, in the Vorticella (Fig. 133) and in some Fig. 134. Polyps (Fig. 134), and sometimes...show more

Product details

  • Paperback | 80 pages
  • 189 x 246 x 4mm | 159g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236739892
  • 9781236739896