the Giliate Infusoria. By G. J. AUman. 185 
being liomologically identified with the orifices of the same name in 
the higher animals, Haeckel proposes for them the terms " Gyto- 
stoma " and " Cijtopyger 
So also the presence of a contractile vesicle and of other vacuoles 
affords no solid argument against the unicellularity of the Infusoria. 
The physiological significance of the contractile vesicles has been 
variously interpreted. In certain cases a communication with the 
exterior appears to have been demonstrated, and Haeckel regards 
them as combining two different functions of nutrition, namely, 
respiration and excretion. They are in all cases destitute of proper 
walls, and they have been long recognized as morphologically 
nothing more than lacunse filled with fluid. Kegular contractile 
vesicles differing in no respect from those of the ciliate Infusoria are 
often found in the Flagellata and in the swarmspores of many Algae. 
Besides the constant and regular contracting vacuoles, there 
occur also others less constant and less regularly contracting. 
These are found in the softer endoplasm, while the constant and 
regularly contracting vacuoles occur for the most part in the firmer 
exoplasm. One is just as much a wall-less vacuole as the other, 
and the difference 'between them is to be traced to the difference of 
consistence in the surrounding protoplasm. Haeckel regards the 
less constant ones as the original form from which the others have 
been phylogenetically derived, that is, by a process of inheritance 
and modification through descent. 
The last and most important of the parts which enter into the 
formation of the Infusorium body, namely, the nucleus, is next 
discussed. Viewed from a morphological point, it has been already 
demonstrated that the nucleus is in all Ciliata originally a single 
simple structure, resembling in this respect a true cell-nucleus. 
As the Infusorium body approaches maturity we find that with its 
advancing differentiation peculiar changes occur in the nucleus just 
as in the rest of the protoplasm, but these changes are entirely 
paralleled by differentiation phenomena which are known in other 
undoubted cell-nuclei, as, for example, in the germinal vesicle of 
many animals, in the nuclei of many unicellular plants, the nuclei 
of many parenchyma cells of the higher plants, and the nuclei of 
many nerve-cells. The mature Infusorium nucleus is often vesicle- 
like, and consists of a delicate investing membrane and fine granular 
contents, precisely as in the differentiated nucleus of many other 
cells. In many Ciliata, if not in all, there is within the young- 
nucleus a dark, more refringent corpuscle, which has quite the 
same relations as the nucleolus of a true cell-nucleus. 
Eegarded from a physiological, no less than from a morphological 
point of view, the Infusorium nucleus and true cell-nucleus admit 
of a close comparison with one another. It may be considered as 
established by the concurrent observations of all investigators, that 
