Text book of zoology / by J.E.V. Boas ; translated by J.W. Kirkaldy and E.C. Pollard.

  • Johan Erik Vesti Boas
Date:
1896
Catalogue details

Licence: Public Domain Mark

Credit: Text book of zoology / by J.E.V. Boas ; translated by J.W. Kirkaldy and E.C. Pollard. Source: Wellcome Collection.

    28/582 page 6
    and the halves of the chromosomes, apparently, are (Fig. 3, 4) thereby drawn away from each other, so as to form two separate groups (Fig. 3, 5). Each group is the beginning of a new nucleus, for its chromosomes unite again to form a new network, and a nuclear membrane arises round it (Fig, 3, 6). Before this happens, however, the protoplasm begins to divide into two parts corre- sponding to the new nuclei. 2 c 3 Fig. 3. Diagram of indirect nuclear division, c centrosome. See text. 5 G Each cell of the animal body has an entity of its own; but it differs from the Amoeba, in that it is a member of, and to a certain extent subordinate to, a great whole. The degree of its independence varies, however, very considerably. Some cells, called wandering cells, retain throughout life a very considerable freedom, and, in nearly all respects, remain on a level with the Amoeba. They have the power of protruding pseudopodia, and each moves about by itself, freely, in the spaces of the body: moreover, whilst most other cells (see the section on the alimentary canal) can only absorb food in a liquid form, the wandering cells can also take up hard particles and dissolve them. Sometimes this peculiarity seems to be exerted even against the organism itself: for instance, in those cases where (as in the metamorphosis of Insects) some organs atrophy— without the death of the creature itself—the wandering cells eat up the dead parts and digest them. They devour also foreign bodies, such as Bacteria, which have got into the body. The blood corpuscles of most invertebrate animals,* and the white blood corpuscles of the Vertebrata, are wandering cells. There are still other free cells, viz., the red blood corpuscles of Vertebrates, which # All the Metazoa, with the exception of the Vertebrata, belong to this group.
    digitised image 1
    digitised image 2
    digitised image 3