. The Annals and magazine of natural history; zoology, botany, and geology. Natural history; Zoology; Botany; Geology. 74 Dr. R, P. Cowles on the Body-cavities and I believe that the cavity of the trunk is formed in the following manner:—As the tentacles grow out and increase in number the posterior region of the larva about the rectum increases greatly in length. In doing the latter the meso- dermal lining of the collar is drawn away from the somatic Fi?. 3. Fi- 2. Vny. 2.—Longitudinal section through young larva, not quite sagittal, X 704. , collar-cavity; g., ganglion; m.^, mesentery be-
. The Annals and magazine of natural history; zoology, botany, and geology. Natural history; Zoology; Botany; Geology. 74 Dr. R, P. Cowles on the Body-cavities and I believe that the cavity of the trunk is formed in the following manner:—As the tentacles grow out and increase in number the posterior region of the larva about the rectum increases greatly in length. In doing the latter the meso- dermal lining of the collar is drawn away from the somatic Fi?. 3. Fi- 2. Vny. 2.—Longitudinal section through young larva, not quite sagittal, X 704. , collar-cavity; g., ganglion; m.^, mesentery be- tween lobe- and collar-cavities; , nephridial pit; , cavity of preorallobe. Fig. .3.—Young larva of Phoronis architecta ; three pairs of tentacles and beginnings of the fourth pair, X 225. , collar-cavity ; , excretory cells ; f/., ganglion ; -jh}, mesentery between lobe- and collar-cavities; ?«.", mesentery between collar- and trunk- cavities ; t., tentacle ; , cavity of trunk. wall in the region back of the tentacular band, and a cavity is left containing the rectum, part of the stomach, and the proximal part of the nephridial diverticula. At the same time this is taking place certain cells, which may iiave their origin from the base of the nephridial diverticula, give rise to the lining of the cavity of the trunk. As to the manner of the origin of these cells, 1 am still in doubt. I have not been able to find two coelomic sacs which Hatschek has figured, and I have hunted for them in larvae where the diverticula. 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 London, Taylor and Francis, Ltd
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