from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. Having a form of egg cleavage where only a small disc separates from the rest of the egg, associated with osseous fishes.
from the GNU version of the Collaborative International Dictionary of English
- adj. Applied to a form of egg cleavage seen in osseous fishes, which occurs only in a small disk that separates from the rest of the egg.
from The Century Dictionary and Cyclopedia
- Undergoing discoidal segmentation of the vitellus: applied to those meroblastic eggs which thereby produce a discogastrula in germinating.
The gastrulation of the discoblastic ova, which chiefly concerns us, offers serious difficulties to microscopic investigation and philosophic consideration.
Hence I had, in 1875 (in my essay on The Gastrula and Ovum-segmentation of Animals), counted the monotremes among the discoblastic vertebrates.
Although the mass of the food-yelk may be very large in the ova of the discoblastic vertebrates, nevertheless in every case a blastula is developed from the morula, as in the holoblastic ova.
According as the yelk-food accumulates at the centre or at the side of the ovum, we distinguish two groups of dividing ova, periblastic and discoblastic.
The primitive fishes (Selachii), which we must regard as the ancestral group of the true fishes, were generally considered, until a short time ago, to be discoblastic.
The wide comparative studies of the scientists I have named have further shown that in the case of the discoblastic higher vertebrates
(Lepidosteus), approaches the osseous fishes, and is discoblastic like them.
In the discoblastic ova the food-yelk gathers at one side, at the vegetal or lower pole of the vertical axis, while the nucleus of the ovum and the great bulk of the formative yelk lie at the upper or animal pole (hence these ova are also called