. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. OBSERVATIONS ON HYDRA AND PELMATOHYDKA. 427 They migrate down the lumen of the tentacle (Fig. i, 5). Now the mesoglea breaks or is resorbed (Fig. i, C) and the endo- dermal elements apparently have little trouble in finding their way to the coelenteron. The cellular masses of ectoderm, spheroidal in shape and often with contained nematocysts, together with the above mentioned dedifferentiated endo-epi- thelial masses, may be found in the coelenteron as far down as the basal disc. Thus the surface of the tentacle is decreased
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. OBSERVATIONS ON HYDRA AND PELMATOHYDKA. 427 They migrate down the lumen of the tentacle (Fig. i, 5). Now the mesoglea breaks or is resorbed (Fig. i, C) and the endo- dermal elements apparently have little trouble in finding their way to the coelenteron. The cellular masses of ectoderm, spheroidal in shape and often with contained nematocysts, together with the above mentioned dedifferentiated endo-epi- thelial masses, may be found in the coelenteron as far down as the basal disc. Thus the surface of the tentacle is decreased. To use the language of Huxley and DeBeer ('23) in describing a similar phenomenon in Obelia and Campanularia, "The ecto- dermal cells may be compared with that of a rear guard, retreat- ing yet always maintaining an unbroken ; These histo- logical details serve as a final criterion for determining whether dedifferentiation and resorption have taken place. But with the aid of low magnification, one can see that, as resorption proceeds, the tips of the tentacles increase in diameter, and finally appear knobbed and the involved area becomes darker and darker, The endodermal cells lining the tentacles are normally highly vacuolated. These cells, however, appropriate relatively much food during the later stages of resorption. It is certain that this dedifferentiated and resorbed tissue is used as food by the animal because nematocysts in various stages of digestion may be found in the epithelio-muscular cells in all parts of the endoderm. This confirms Kepner and Jester ('23) in their minor claim that the ingested parts were used as food; but Kepner and Jester were misled by the occasional biting off of the tentacles. Dedifferentiation and resorption are the usual reaction. Since it was seen that both the cells of the ectoderm and the endoderm of the tentacles were almost exactly like those of the lateral walls of the basal one third of hydra, dedifferentiation and
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
