the Ciliate Infusoria. By G. J. Allman. 189 
The union of the Protista into a distinct kingdom equivalent in 
systematic value with the animal or vegetable kingdom, can, how- 
ever, scarcely be maintained. We already know enough of some 
of them to justify our assigning these to one or other of the two 
generally accepted organic kingdoms ; and there can be little doubt 
that, did we know the whole history of the others, and were able 
to formulate the essential difference between the animal and vege- 
table kingdom, these, too, would be referred without hesitation 
either to the one or to the other, some passing to the former and 
others to the latter. The group of the Protista is thus at best but 
a provisional one, based partly on our ignorance of the structure 
and life history of the beings which compose it, and partly on our 
inability to assign to the animal its essential difference from the 
plant. Haeckel, however, has done well in specially directing 
attention to it, and in his admirable researches on many of the 
organisms which he has thus grouped together he has largely 
contributed to our knowledge of living forms. 
I have thus dwelt at considerable length upon this important 
paper of Haeckel’s, because I think that it not only brings out in a 
clear light the essential features of infusorial structure and physi- 
ology as demonstrated by recent research, but that it goes far to 
set at rest the controversy regarding the unicellularity and multi- 
cellularity of the Infusoria. 
Balbiani * has quite recently published a very interesting account 
of the remarkable Infusorium long ago described by 0. F. Muller 
under the name of Vorticella nassuta, and more recently taken by 
Stein as the type of his genus Didinium. 
The animal (Fig. 5), which is somewhat barrel-shaped, with an 
anterior and a posterior wreath of cilia, has one end continued into a 
proboscis-like projection which carries the oral orifice on its summit, 
while an anal orifice is situated on the point diametrically opposite 
to this. There is a very distinct cuticle, though the rest of the 
cortical layer is very thin, and can scarcely be optically distinguished 
from the internal parenchyma, which exhibits manifest currents of 
rotation. These flow in a continuous sheet along the walls from 
the anal towards the oral side, and on arriving at the mouth turn in 
towards the axis and then flow backwards along this until they 
complete the circuit by once more reaching the anal side of the 
body. No trichocysts are developed in the walls of the body. The 
contractile vesicle is large, and is situated near the anal end; it 
presents very distinct pulsations, and Balbiani is disposed to believe 
in a communication between it and the exterior. 
During the act of digestion a tubular cavity can be seen running 
through the axis of the body, and connecting the oral and anal 
* ‘Arch. Zool. Exper.,’ vol. ii. 
