. Chimæroid fishes and their development. Fishes; Chimaeridae. DETAILS OF LATER EMBRYO. 105 loosened at several points, giving the wav\' contour noted in the figure of the entire embryo. The arrangement of the vessels is clearly shown, and one traces the posterior umbilical veins and the anterior vitelline arteries. At first sight the yolk-sac seemed to be attached anteriorly throughout the length of the heart region. Later examination, however, showed that a single stalk, albeit a very short one, connected the sac with the trunk in a fashion very much as in the young shark. {Cf. plate VIII, f
. Chimæroid fishes and their development. Fishes; Chimaeridae. DETAILS OF LATER EMBRYO. 105 loosened at several points, giving the wav\' contour noted in the figure of the entire embryo. The arrangement of the vessels is clearly shown, and one traces the posterior umbilical veins and the anterior vitelline arteries. At first sight the yolk-sac seemed to be attached anteriorly throughout the length of the heart region. Later examination, however, showed that a single stalk, albeit a very short one, connected the sac with the trunk in a fashion very much as in the young shark. {Cf. plate VIII, fig. 49''). (7) The lateral line sys- tem of organs is already established. At either side of the ej'e sensory pits are present and the backward growth of the lateral line could be traced as far as the anal region. DETAILS OF THE FOREGOING EMBRYO. In the sections, figs. 80-83, are shown details of the foregoing embryo. In the first of these (fig. 80), in the eye structures one observes the proportionally enormous size of the lens. Particularly noticeable, also, are the elaborately branching vessels lying be- tween the eye and the mid- brain {i>,v), a symptom again of the embryo's precocious growth. In the following section (fig. 81) the spiracle {s) is seen to be continuous. Sections through an external gill-filament show, even more conspicuously than in shark, the presence of both vein and artery {a, z). In the same section we observe one of the blood-filled dilatations {d), which have already been commented upon. This appears at or near the end of the gill-filament. In fig. 82, a section through the pelvic region just anterior to the anus, we observe on the right side the opening of a segmental duct at sd. Beside it, at mt, appears a mesonephric tubule. On the opposite side of the body a corresponding tubule, ;;//*, opens directly into the body cavity. One observes in the same section a dilated caudal vein at cv, and above it the caudal arter}^ In the section, fig. 83, we
Size: 1493px × 1674px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectfishes, bookyear1906
