258 THE AMERICAN NATURALIST. (VoL. XXXIII. 
At 38° C. polyps did not regenerate, but died. Hence the optimum 
lies between 30° and 38° C. A. grisea, at the room temperature | 
(18-24° C.), regenerates more slowly than Æ. viridis; but it is rela- 
tively more accelerated by the increased temperature. 
Experiments upon the relative effect of light of different wave- 
lengths resulted negatively; but these experiments do not seem to 
have been carried out very thoroughly. 
Organisms and Oxygen.' — That oxygen is necessary to the life of 
organisms is a dogma which seemed to have received a severe shock 
when the facts of anzerobic bacteria (which are killed by the presence 
of free oxygen) became known. 
Errara points out that after all this necessity for oxygen is one of 
degree. As there are certain species which need a large amount of 
oxygen, so there are others which have a very low optimum of oxygen 
supply; such are the anærobic forms. In the presence of a larger 
amount of oxygen they thrive less well, and may even die. 
The Phylogenetic Significance of Protozoan Nuclei.*— The 
minute structure of the nuclei of Tetramitus, Microglena, Synura, 
Chilomonas, Trachelomonas, Stylonychia, Amoeba, Euglena, Cera- 
tium, Peridinium, and Noctiluca has been carefully investigated by 
Mr. G. N. Calkins. A considerable variety of nuclear types is 
recognized, the simplest of which is the distributed nucleus, which 
consists of isolated chromatin granules scattered about in the cell. 
Nuclear membrane and linin threads are absent; there is, however, a 
cytoplasmic body near which the chromatin granules gather at the 
time of division ; the activity of this body is analogous to that of the 
centrosphere of more highly organized cells. Nuclear conditions of 
this type are found in Tetramitus. A higher form of structure is 
found in the “intermediate ” type of nucleus which occurs in Micro- 
glena, Synura, Chilomonas, the euglenoids, in which the attraction- 
sphere is intranuclear, definite in form, deeply staining and active, 
and the chromatin granules are massed about it permanently, as in 
the forms just mentioned, or only during division, as in Paramceba. 
A nuclear membrane is found in the case of some nuclei of this 
“intermediate type.” In higher types of nuclei the attraction-sphere 
is no longer intranuclear, but this position of vantage is taken by 
ara, L. Tous les ppi vivants ont-ils besoin d'oxygène libre? Rev. 
n aaan (4) X, 688, 689, 26 Nov., 1898. 
kins, Gary N. The S aedi Significance of Certain Protozoan Nuclei, 
is N. Y. Acad. Sci., vol. xi (1898), pp. 379-400, Pl. XXXV. 
