On the embryology of Bdellostoma stouti; a general account of myxinoid development from the egg and segmentation to hatching

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1899 Excerpt: ...however that I am unable to understand what Prof. Whitman means in the passage cited, for I think it will be very difficult for embryologists to believe that the cleavage cavity is not an homologous structure throughout the Anamnia, That intercellular spaces have from the time of the earliest cleavages produced a typical cavity in Amphioxua has been as far as I am aware a fact unquestioned since the time of the pioneer observations of Kowalewsky. And that cleavage cavities, primarily intercellular, may secondarily be augmented by the absorption of vacuoles is also a fact which few embryologists will question. 32 3. Blastula. In the section figured in PI. XX, Fig. 78, is represented a stage which I interpret as late blastula. It is taken from a series which unfortunately is incomplete, and in which the yolk region is seriously defective. The section represented passes transversely through the anterior end of the egg, slightly in front of the opercular ring. The central portion of the figure included within the dotted line, which arises at the surface between the points is drawn from a single section: the surrounding portion is figured from an adjacent section in which the yolk is retained. Incomplete as this stage is it demonstrates that the cell mass is many celled in thickness and that in the blastula there is no abrupt transition between yolk and blastomeres. It also contributes evidence, although by no means complete, that the downgrowth of the cellular cap is early asymmetrical--a condition which seems to me an improbable one, judged solely from a priori evidence. This section illustrates again the size of the intercellular spaces, the clear peripheral zone of the blastomeres and sharply marked cell walls. Fig. 24. Sagittal section of gastrula of PI. XX...