Mammalia / by Frank Evers Beddard.

  • Frank Evers Beddard
Date:
1902
Catalogue details

Licence: Public Domain Mark

Credit: Mammalia / by Frank Evers Beddard. Source: Wellcome Collection.

    88/626 page 72
    discovery rests with Owen and with Professor Poulton, who pointed out in 1884,1 that the ovum of Ornithorliynclms is very large as compared with those of other Mammalia (6 mm. as against -2 mm.), that it is filled with yolk, and that it completely fills the follicle, being surrounded by two layers of follicular cells only. This latter fact was proved by Caldwell. Subse¬ quently Gyldberg2 and 13 described the ovarian ovum of Echidna, Fig. 46.—Ovarian egg of Echidna, b, Basilar membrane ; fe, follicular epithelium ; o, oil globules ; vm, vitelline membrane ; yx, y2, yolk. (Partly after Caldwell.) showing it to be identical with that of Ornitliorhynchus. Later still a more elaborate and beautifully illustrated paper was pub¬ lished by Caldwell4 upon the early stages of development in the Monotremata and Marsupials, in which the ovum of the former was accurately described (see Pig. 46). In the particulars mentioned above, the ovum of the Monotremata is practically identical with that of the large-yolked ova of the Sauropsida. 1 Quart. Journ. Micr. Sci. xxiv. 1884, p. 9. 2 S.B. Jen. Gesells. 1885, p. 1. 3 Proc. Roy. Phys. Soc. Edin. viii. 1885, p. 354. 4 Phil. Trans, clxxviii. 1887, p. 463.
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