On the histology of Hydra fusca / by T. Jeffery Parker ; communicated by Professor Huxley.

  • Thomas Jeffery Parker
Date:
1880
Catalogue details

Licence: Public Domain Mark

Credit: On the histology of Hydra fusca / by T. Jeffery Parker ; communicated by Professor Huxley. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    will hare been shown to exhibit a process of alimentation identical with that described by Metschinkoff, in the lower Turbellaria and in sponges.* The Russian observer describes the complete obliteration, during digestion, of the digestive cavity in the Turbellarians, and of the canals in the sponges; and, in the former as well as the latter, he has undoubted evidence of the actual ingestion of solid particles by the endoderm cells. It would seem, therefore, that Hydra adds another instance to the two already brought forward by MetschnikofF, of a Metazoon exhibit- ing what is usually considered to be a distinctively Protozoan mode of digestion. It is quite possible that a preliminary disintegration of the animals taken in is performed by juices secreted by the endoderm cells, but the final digestion seems to take place in the actual protoplasm of the cells, into which the food articles are taken in the solid form. The endoderm cells of the tentacles resemble those of the proximal and of the body in possessing larger vacuoles (fig. 5). Their nuclei are in some instances, although not constantly, simple and non-nucleo- late like those of the ectoderm cells for the same region (fig. 5). Finally, I have been able fully to confirm Professor Huxley’s state- ment! as to the presence of nematocysts in the endoderm (fig. 1, n), a statement which, as far as I am aware, has not been made, with regard to Hydra, by any other writer on the subject. This fact is, like the absence of interstitial tissue in the tentacles, an argument against Kleinenberg’s view that the tissue is the sole source of the nema- tocysts. 4. Methods.—For sections, the Hydros were either killed with hot water, and placed in Kleinenberg’s picric acid for two hours, or were placed alive in ammonic bichromate, 1 per cent.—which always kills them in the half extended condition—and kept in it for two or three days. In either case they were afterwards transferred to 50 per cent, alcohol, and then placed successively in 75 per cent., 90 per cent., and absolute alcohol. The specimens were stained either with carmine or picrocarmine, and imbedded in cacao butter, after soaking for a short time first in oil of cloves and then in melted cacao butter. By this means they became so thoroughly permeated with the imbedding material that they could bo cut without the loss of a single section ; even longitudinal sections of the tentacles could be made with ease. For teasing I employed ammonic bichromate, acetic acid (0‘5 per cent.), or osmic acid (1 per cent.), and for this purpose the specimens were not transferred to alcohol, but to weak glycerine (equal parts of glycerine and water ), in which they were teased out. * “ Zool. Anzeiger,” Bd. I (1878), p. 387, and “ Zeitsch. f. wiss. Zool.” Bd. xxxii (1879). It need hardly be said that the above view of the physiology of digestion in Hydra was suggested by these papers of Metschinkoff’s. t Huxley and Martin, “ Elementary Biology,” p. 100.
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