Zoology : an elementary text-book / [Sir A.E. Shipley].

  • Arthur Shipley
Date:
1920
Catalogue details

Licence: Public Domain Mark

Credit: Zoology : an elementary text-book / [Sir A.E. Shipley]. Source: Wellcome Collection.

    54/780 (page 30)
    comparatively common inhabitants of our ditches. The first is, however, exceedingly minute, not more than xoVoth of an inch in diameter and possesses only a single nucleus, whereas the second is large enough to be just visible to the naked eye, and has about 200 nuclei. There is here repetition of the nuclei, but no division of the protoplasm, whereas in Polystomella there is segmentation of the protoplasm, hut no corresponding multiplication of the nuclei. If both were to occur simultaneously and to correspond so that the body were to consist of a number of segments of protoplasm, each Fig. 8. ActinopTirys sol x about 800. From Broun. 1. Ectoplasm. 2. Endoplasm. 3. Contractile vacuole. 4. Food vacuole. 5. Nucleus. 6. Axis of a pseudopodium, stiffer than the protoplasm which covers it. with its nucleus, the animal would be said to be multicellular, each unit being spoken of as a cell; but it would no longer be a Protozoon. Actinosphaerium can retract its pseudopodia and encyst itself. The cyst wall contains numerous spicules of silica. This cyst is called the mother-cyst. The nuclei are now rapidly absorbed till only a few of the original 200 remain. The protoplasm then divides into masses each with one of these residual nuclei. These masses secrete round themselves the primary daughter-cysts. The protoplasm inside each daughter cyst divides into two spores which secrete round themselves secondary cysts. The nucleus of each