ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
519 
Tunicata. 
Plankton Thaliacea.* — Herr J. Reibisch reviews the work of 
M. P. A. Transtedt on the systematic relations of the Plankton Thaliacea, 
and that of 0. Apstein on their distribution. Only two subgenera — 
Cyclosalpa and Salpa — are recognised. The genera Jasis, Thalia , and 
Pegea are based upon wholly external characters ; but the species of 
Salpa s. str. may be brought together, and to them Apstein applies the 
title Cylindrica. In the unsymmetrical Salpae, the individuals of the 
two rows are not congruent, but mirror one another as regards their 
musculature. Even in the symmetrical Salpae, there is no perfect con- 
gruence, since in both rows the embryo always lies on the right. 
Apstein believes that the buds are at first congruent, and become 
secondarily unlike through their relations to the stolon. 
The aggregate forms are much more numerous than the solitary 
forms, perhaps because each chain-individual forms only 1-5 embryos, 
while the solitary form gives rise only to a chain with a considerable 
number of individuals. 
As is well known, the Salpae are mainly confined to warm water, to 
near the tropics, or to such currents as the Gulf Stream. One species, 
S. Hensenii, frequents the coast ; all others are pelagic. Occurrence at 
considerable depths is very rare. 
Isolated Blastomeres in Ascidians.f — Hr. H. Driesch finds that an 
isolated blastomere of the egg of Phallusia mammilata may, as in Echi- 
noderms, form a complete individual. Complete larvae may arise from 
one of the first two cleavage cells, and are about half the normal size. 
The sensory and adhesive organs may be in part deficient, as is the case 
in larvae reared from whole eggs when exposed to advrese circumstances. 
There is no semi-morula. Roux in the frog, and Cliabry in the Ascidian, 
as well as Chun in Ctenophores, found, it will be remembered, cases 
where an isolated blastomere did not make a complete individual, but 
only a half or a partial one, but the differences in the methods employed 
by Chabry and Driesch are so considerable that we can scarcely expect 
a very close agreement in the results. 
Budding in Perophora.f — Mr. G. Lefevre has made a study of the 
development of the buds of this Ascidian, which was found growing 
luxuriantly on the wharf-piles at Beaufort, N.C. He finds that, by a 
peculiar process of rotation of the endodermal vesicle through a right 
angle, the thickened right wall of the vesicle is carried down to the ven- 
tral side of the bud-rudiment, where it forms the floor of the future 
pharynx. This process seems to be due to the rapid growth and flatten- 
ing of the cells which compose the vesicle, except in its thickened por- 
tion. The first organ to appear is the pericardial rudiment, and it is 
formed from the free cells of the blood. The peribranchial sacs arise 
asymmetrically. No epicardium is present, so that in this respect 
Perophora differs strikingly from some other Ascidians. The endostyle 
appears early as a longitudinal groove in the middle of the thickened 
portion of the inner vesicle. From its position on the right side it is 
moved down to the ventral mid- line by the rotation of the vesicle. The 
* Biol. Centralbl., xv. (1895) pp. 93-6. 
f Arch. f. entw. Mech. d. Organismen, 1895. See Amer. Natural., xxix. (1895) 
pp. 500-1. J Johns Hopkins Univ. Circ , xiv. (1895) pp. 75-7 (5 figs.). 
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