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Some observations on depressive phenomena in Hydra vulgaris


, : Some observations on depressive phenomena in Hydra vulgaris. Riv Biol [Perugia] 50(4): 327-343

The phenomenon of "depression," as Hertwig first termed it, is discussed in the light of the author's personal observations on Hydra vulgaris. Of all the possible causal factors considered[long dash] temperature, nutrition, sudden changing of the culture liquid, population density, fouling of the medium[long dash]the most important proved to be fouling, whether produced by fermentation of food or by traces of toxic substances. A further endogenous cause seemed to be the existence of anomalies and malformations. These always followed ovogenetic sexual periods, and the author believes there may be a causal connection, related to metabolic factors, among the various physiologic states noted during the life cycle of clones of Hydra. The depressed or flourishing condition of a colony is reflected in the emission into the culture liquid of substances capable of inducing or arresting the depressive phenomena. Thus, when small lots of depressed individuals were placed in a medium containing a few healthy individuals, the latter always succumbed to depression. The signs of depression are shortening and terminal enlargement of the tentacles. Histologically, they are expressed in exfoliation of the gastrodermis, which proceeds in an apico-basal direction. Only later do degenerative signs appear in the mesogloea and epidermis. The depressive process may lead to the complete disintegration of the polyps, but recovery from less serious depression is possible. In recovery, the tissues show signs of regenerative activity, especially in the epidermis; this regeneration seems to be the work of the interstitial cells. Buds of depressed specimens showed a striking resistance to depression.

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