. Chimæroid fishes and their development. Fishes; Chimaeridae. PRECOCIOUS DEVELOPMENT IN EARLY EMBRYO. n. embryi Bd. xxxix, Taf. in), we note that tlie Chim;e- roid although smaller is much less flattened out; that the gut which is flattened against the yolk in the elasmobranch is in Chimaera defi- nitely formed and provided with a distinct lumen; that the lateral contour of the embryo's body in Chima'ra is already developed, the ectoderm in the hinder region fusing with the entoderm; that the yolk entoblast thickens in the median axial line, a feature lacking in the shark, but important doubt
. Chimæroid fishes and their development. Fishes; Chimaeridae. PRECOCIOUS DEVELOPMENT IN EARLY EMBRYO. n. embryi Bd. xxxix, Taf. in), we note that tlie Chim;e- roid although smaller is much less flattened out; that the gut which is flattened against the yolk in the elasmobranch is in Chimaera defi- nitely formed and provided with a distinct lumen; that the lateral contour of the embryo's body in Chima'ra is already developed, the ectoderm in the hinder region fusing with the entoderm; that the yolk entoblast thickens in the median axial line, a feature lacking in the shark, but important doubtless in the early assimilation of the yolk. From the foregoing details one is led to conclude that in Chimjera '' precocious segre- gation" has been developed to a noteworthy degree. In spite of the small size of the both relatively and actually, it has already made strides in the direction of attaining its definite form, outstrip- ping in these regards the elasmo- branch ; thus it has already dcveloiJcd gut outline, definitely arranged the mesoblast, separated ju'actically the sides of the embryo from the blasto- derm, and has s])ecially concentrated the yolk entoblast in the axial region. Accordingly, in these regards, Chi- maera stands separate from the elas- mobranchs; transitional, however, is Callorhynchus, judging from figures recently given by Schauinsland (c. g., in his plate xii). An idea of the complicated nature of the blastoderm at this stage (plate v, fig. 35), both in itself and in its relation to the yolk, may be had by examination of fig. 70. This repre- '^ sents part of a section which passes through the blastoderm transversely, somewhat in front of the embryo. Fig. 70.—Detail ol section of preceding embryo. The section is transverse and passes near middle ot blastoderm. It shows particularly the early differentiation of the vacuolar area, a-b. Peripheral zone of blaslod elm ; b-c. central region of blastotferm ; 1-5, centers of proliferation of ecto-
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectfishes, bookyear1906
