ZOOLOGY AND BOTANY, MICROSCOPY. ETC. 
493 
Holothuroids and Crinoids (Monorchonia of Haeckel), and the other 
including Ophiuroids, Asteroids, and Echinoids (Pentorchonia of 
Haeckel). 
Ccelentera. 
Structure of Two Zoantharia.* — Prof. A. R. v. Heider describes 
the anatomy of two forms from the collection of the * Yettor Pisani.* 
The one belongs to the genus Palythoa , and is apparently a new species 
— P. brasiliensis. It is a colonial form with the mesogloea and cceno- 
chyme filled with incrusting sand-particles which greatly interfere with 
the process of section-cutting. The polyps are separated from one 
another only by a thin mesogloea, invested on both sides with endoderm, 
and continuous with the coenochyme which fills up the angles between 
the contiguous polyps, and also with the basal coenochyme. Both 
coenochyme and mesogloea have the same structure, being traversed by 
canals and impregnated with foreign particles. In the upper part of 
the polyp lies the sphincter, which is mesodermal and only slightly 
developed. The mesogloea also contains in certain regions fibres and 
cells. The fibres the author believes to be the means of communica- 
tion between ectoderm and muscles, and therefore to be of the nature of 
nerves. The cells are connective tissue cells, probably originating from 
the ectoderm. On account of the bad preservation little could be made 
of the ectoderm. The cells on the tentacles and in the region of the disc 
were filled with zooxanthellae. The author believes that the ectoderm- 
cells of the upper part of the wall of the polyps take up the foreign 
particles which fill the mesogloea, just as the cells of the tentacles and 
disc take up zooxanthellae. Practically nothing was made of the 
endoderm. 
The other form, apparently Gemmaria variabilis Duerd., is likewise 
colonial and incrusted. The incrustation is confined to the walls of the 
polyps, and coenochyme is ‘absent between them, so that they are at- 
tached only by a basal sheet. Zooxanthellae are abundant in the ecto- 
derm, but the abundance of sand-particles made an investigation of the 
histology impossible. 
Regeneration in Hydra.f — H. W. Rand finds that when a number 
of individuals of U. viridis are bereft of their tentacles, the number of 
regenerated tentacles is always rather less than the original sum. The 
difference between the original average number of tentacles and the 
average number of regenerated tentacles is greater in proportion to 
the original number. The number of regenerated tentacles seems to 
depend in part on the size of the fragment. A whole polyp regenerates 
more than a half does, and a half more than a quarter. In cases of 
longitudinal halving the original number is restored by each half. 
Like other modern experimenters, Rand failed to rear a polyp from an 
isolated tentacle, as Rosel von Rosenhof says he did with H. grisea. 
The author discusses also the “ regulative processes ” in regeneration. 
Loss of Ectoderm in Hydra viridis.J — Mr. W. L. Tower has ob- 
served a very curious reaction in hydra when placed on the stage of a 
* Zeitschr. f. wiss. ZooL, lxvi. (1899) pp. 269-88 (2 pis.). 
t Arch. Entwickmech.; viii. (1899) pp. 1-34 (4 pis.). See Zool. Centralbl., vi. 
(1899) pp. 385-6. X Amer. Nat., xxxiii. (1899) pp. 505-9 (2 figs.). 
1899 2 l 
