. Analysis of development. Embryology; Embryology. 298 Embryogenesis: Progressive Differentiation poration of marked material from the yolk by the blastodisc. In the early days of morphogenetic experi- mentation (Morgan, 1893; also Lewis, '12, Hoadley, '28) it was established that con- siderable cytoplasm of the uncleaved blasto- derm in Fundulus may be removed by punc- ture without disturbing subsequent develop- ment. More recently (Tung and Tung, '44), there has been a report of puncturing the goldfish egg in the equatorial region, just before fertilization while the protoplasm. *f-:^^- :..^
. Analysis of development. Embryology; Embryology. 298 Embryogenesis: Progressive Differentiation poration of marked material from the yolk by the blastodisc. In the early days of morphogenetic experi- mentation (Morgan, 1893; also Lewis, '12, Hoadley, '28) it was established that con- siderable cytoplasm of the uncleaved blasto- derm in Fundulus may be removed by punc- ture without disturbing subsequent develop- ment. More recently (Tung and Tung, '44), there has been a report of puncturing the goldfish egg in the equatorial region, just before fertilization while the protoplasm. *f-:^^- :..^r^ Fig. 108. From top to bottom: a giant embryo of Carassius produced by fusion of two four-celled eggs; a normal embryo of corresponding stage; and an embryo formed from half an egg (cf. Fig. 110). (Redrawn from Tung and Tung, '44, Fig. 16.) is still flowing upward to form the blasto- disc. A normal embryo may form from as little as one-half the material of the egg under these circumstances. All fragments, however, do not form normal or nearly nor- mal embryos: over half form monstrosities where head, trunk or tail predominates; in a few, gastrulation is suppressed. Clearly, some sort of spatially arranged system is being displaced in these cases. Polar arrangement in the vast fluid ovar- ian egg of the bird is even more impressive than it is in the case of the fish. The eccen- tricity of the nucleus has an obvious intimate relation to the pattern of yolk deposition. It must be recalled, when discussing axiation in the meroblastic eggs, that as yolk content becomes more extreme in proportion to pro- toplasm, the animal-vegetal axis tends more and more to represent the future dorso- ventral axis of the embryo, while the antero- posterior axis of the embryo proper is repre- sented by a smaller and smaller meridional arc of the egg. In the pigeon, Bartelmez ('12) has traced not only anteroposterior but left-right axes back to slight eccentricities of the nucleus in early oocyte s
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