268 DR. ZENKER, ON INFUSORIA. 
wardly, at once upsets the theory that its function is that of a 
circulatory organ or heart. But the question then arises, 
What is the nature of the fluid which is thus continually got 
rid of? It is perfectly transparent, and appears of a very pale 
reddish colour. The last circumstance may probably have 
been one reason why zoologists have regarded the fluid as 
spermatic or as blood. So far as I know, Oscar Schmidt was 
the first to observe that the water close to the infusorium was 
also of a reddish hue, owing to the contrast with the bluish 
colour of the animalcule. There appears to be no reason, 
therefore, to suppose that the fluid is anything more than 
plain water; no doubt with respect to this can be entertained 
when we consider the enormous quantity in which it is 
excreted. It is possible, however, that it may occasionally 
contain minute quantities of albuminous compounds (as in 
the instance of Spirostomum ambiguum just cited). 
Water alone could be excreted in such large quantities 
without injury to the organism. The infusoria are capable of 
continually taking in large quantities of water spontaneously 
by the mouth; and the cavity of the body is also entirely 
filled with it. In like manner they are surrounded with 
water on all sides, which may possibly find admittance 
through the skin, even leaving out of question the canals. 
In any case it is important to arrive at a clear notion of the 
various possibilities of the case, since in this phenomenon we 
are concerned with the most active change of matter that 
takes place in the body of the infusoria. 
In the rhizopoda, many of which are likewise furnished 
with a pulsating vesicle, there can be no doubt that the 
external surface, or some part of it, must be the site of imbi- 
bition, since these creatures have no mouth. And a similar 
instance is afforded by the Opalina, astomatous infusoria 
which occur so abundantly in the rectum of the frog, and 
which are furnished with whole series of pulsating vesicles. 
On the other hand it may perhaps be assumed that where the 
outer membrane is of a harder consistence it is rendered unfit 
for the function of absorption. Such would be the case, for 
instance, in the mantle of the Vorticelle and Acinete, in which 
instance it would appear pretty certain that the water finds 
entrance only through the mouth or some analogous organ. 
It is at any rate evident, from the wide distribution and 
fine ramification of the radiating vessels in Bursaria leucas, 
that the water is collected from every part of the walls of the 
body, and consequently that it pervades the entire body of 
the animal, which, to express it in a few words, consists 
merely of an envelope surrounding the large cavity into which 
