. Amphioxus and the ancestry of the vertebrates. Amphioxus; Sea squirts; Hemichordata. 153 DEVELOPMENT OF AMPHIOXUS. of the peritoneal epithelium lining the general body-cavity. The fact that they arise in the way shown by Boveri is one of great morphological importance. In a transverse section of a young individual 5 mm. in length, the primitive sexual cells are to be recognised as a closely packed group of cells, with large nuclei in the lower angle of the myotome ; that is, in the angle formed by the membrane which divides the myocoel from the splanchnocoel, which we may call the intcrcoeli
. Amphioxus and the ancestry of the vertebrates. Amphioxus; Sea squirts; Hemichordata. 153 DEVELOPMENT OF AMPHIOXUS. of the peritoneal epithelium lining the general body-cavity. The fact that they arise in the way shown by Boveri is one of great morphological importance. In a transverse section of a young individual 5 mm. in length, the primitive sexual cells are to be recognised as a closely packed group of cells, with large nuclei in the lower angle of the myotome ; that is, in the angle formed by the membrane which divides the myocoel from the splanchnocoel, which we may call the intcrcoelic membrane, with the cutis (Fig. 85). Since the myotomes of one side alternate with those of the other, so do the centres of. Fig. 86. — Longitudinal views of the developing gonads, obtained by dissecting out the ventral borders of the myotomes. (After Bo\' Primitive sexual cells arising from the myocoelic epithelium ; the nuclei scattered about the surface of the preparations also belong to the myoccelic epithelium. formation of the primitive sexual cells, and in a given section, as in Fig. 85, only one such centre is to be observed on the right or left side of the section, as the case may be. Its actual position in the longitudinal aspect of the myo- tome is shown in Fig. Z6 A, B, and C. The formative centres of the primitive sexual cells lie at first in the ano-le mentioned above, but applied to the posterior faces of the dissepiments between the myotomes (Fig, 86 A). At a somewhat later stage, having slightly increased in bulk, they begin to push the dissepiments before them. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Willey, Arthur, 1867-. New York, London, Macmillan
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishernewyo, bookyear1894
