. Analysis of development. Embryology; Embryology. Teleosts and Birds 301 there is established the elongated blastopore more commonly known as the primitive streak. Figvire 111 is intended to illustrate the broad lines of these morphogenetic dif- ferences during the gastrulation period. The striking features here are the peripheral longitudinal line and its closure hence en- tirely dissociated from the overgrowth of the yolk by the periphery of the blastoderm. The diagrams of Figure , taken from the sequence in Fundukis, can serve as a model for teleost development only in a very B. Fig.
. Analysis of development. Embryology; Embryology. Teleosts and Birds 301 there is established the elongated blastopore more commonly known as the primitive streak. Figvire 111 is intended to illustrate the broad lines of these morphogenetic dif- ferences during the gastrulation period. The striking features here are the peripheral longitudinal line and its closure hence en- tirely dissociated from the overgrowth of the yolk by the periphery of the blastoderm. The diagrams of Figure , taken from the sequence in Fundukis, can serve as a model for teleost development only in a very B. Fig. 111. Diagrams comparing major prospective divisions of the germ in (A) teleost (Fundulus: Oppen- heimer, '37) and (B) chick (Rudnick, '48; Spratt, '52) during gastrulation and later. For obvious reasons most of the yolk mass is omitted in the chick figures. White: ectoderm. Radiating lines in Bl and B2: non- medullary ectoderm. Stippled: superficial material which will later be invaginated. Broken lines: invaginated material. Mesh: extraembryonic ectoderm. Circles: yolk, i, Blastula stage; 2, late gastrula, blastopore nearly closed; 3, embryo formed. position of the material to be invaginated, in the teleost blastoderm, as contrasted with its central-posterior position in the bird; con- versely, the central position of the extra- embryonic material in the fish, and the peripheral location of all extraembryonic material in the bird. The blastopore in the first case is the periphery of the disc; in the second case, it is reduced to a central general way. Fish eggs vary widely in their proportion of protoplasm to yolk, in the relative time necessary for closure of the blastopore, and hence in the relation of axis formation to invagination. The two best-known forms experimentally, Salmo and Fundulus, are widely separated in the series. Figure 112 diagrams comparable stages as regards blastopore closure in these eggs;. Please note that these images are extracted from scanned page im
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Keywords: ., bookcentury1900, bookpublisherphiladelphi, booksubjectembryology
