the Ciliate Infusoria. By G. J. Allman. 177 
of the body, numerous capsules (Figs. 2 a and 2 h) indistinguishable 
from the true ccelenterate thread-cells. These bodies, however, are 
never included in a special investment, and he justly regards their 
presence as affording no argument against the unicellular nature of 
the Infusoria. He lays it down as a probable distinction between the 
trichocysts of the Infusoria and genuine thread-cells, that the former 
have the power of ejecting their contained filament from both ends of 
the capsule, while we know that in the thread-cell it is only one end 
which gives exit to it. This double emission of a filament appears 
to have been observed by Butschli in the trichocysts of a large 
Nassula, hut the distinction is certainly not a generally valid one. 
There is no doubt that in the majority of cases the trichocyst emits 
its filament from only one end of its capsule, exactly as in the 
thread -cells of the Coelenterata, and it is hard to see in what 
respect the bodies noticed by Biitschli in his Polylcricos Swartzii 
essentially differ from true infusorial trichocysts. In conclusion, 
he declares himself strongly in favour of the unicellularity of the 
Infusoria. 
The reproductive process was lately followed by myself through 
some of its stages in a very beautiful Vorticellidan obtained 
abundantly from a pond in Brittany.* The zooids which form the 
colonies in this Infusorium are grouped in spherical clusters on the 
extremities of the branches. They present near the oral end a 
large and very obvious contractile vesicle, and have a long cylin- 
drical nucleus curved in the form of a horseshoe. 
In the internal protoplasm are also imbedded scattered green 
chloropliylloid granules. No trace of the so-called nucleolus was 
present in any of the specimens examined. 
Among the ordinary zooids there were usually some which had 
become encysted in a very remarkable way, and without any 
previous conjugation having been noticed. These encysted forms 
were much larger than the others and had assumed a nearly 
spherical shape ; the peristome and cilia disk had become entirely 
withdrawn, the contractile vesicle was still obvious, but had ceased 
to manifest contractions ; brownish spherical corpuscles with 
granular contents, probably the more or less altered chloropliylloid 
granules of the unencysted zooid, were scattered through the 
parenchyma, and the nucleus was not only distinct, but had 
increased considerably in length. Round the whole a clear gela- 
tinous envelope had become excreted. 
In a later stage there was formed between the gelatinous 
envelope and the cortical layer of the body a strong, dark-brown, 
apparently chitinous case, the surface of which in stages still 
further advanced had become ornamented by very regular hexagonal 
spaces with slightly elevated edges. In this state the chitinous 
* British Association Reports, 1873. 
