132 Proceedings of Royal Society of Edinburgh. [sess. 
logy of the Invertebrata ” (Proc. Roy. Soc. Lond., vol. xliv. p. 325), 
that the five pouches of the stomach of the Asteridea also perform 
the function of kidneys ( i.e ., the digestive apparatus performs a 
dual function). And whatever may he the multitudinous functions 
of the Protozoan contractile vacuoles, one thing is certain, that they 
secrete periodically a waste nitrogenous substance. This nitrogenous 
substance was proved to be uric acid. 
A number of amoebae were placed on a microscopic slide and 
covered by a thin glass slip. Alcohol was run in between the slide 
and cover -slip, so as to kill the organisms. It was found that in 
many cases moderately weak alcohol caused no contraction of the 
vacuole. The alcohol was followed by nitric acid ; the slide gently 
warmed, and, finally, ammonia introduced between the slide and 
cover-slip. In a few minutes, prismatic crystals of murexide * 
having a beautiful reddish-purple colour, made their appearance. 
After the addition of alcohol (as already stated), minute flakes 
could be distinctly seen floating in the fluid of certain contractile 
vacuoles. Bearing in mind the murexide reaction, there is every 
reason to believe that these flakes are nothing more or less than 
minute crystals of uric acid. 
These reactions have been constantly repeated during the past 
few years, and always with the same results. 
It appears, from close microscopic observations, there are times 
when the fluid of the contractile vacuoles does not contain 
the least trace of uric acid. Most likely the Protozoan vacuoles 
perform more than one function. It is possible that they represent 
“ an internal respiratory apparatus ” as well as an excretory organ 
or ££ kidney.” There is little doubt that we have in the contractile 
vacuole of the amoeba a primitive kidney or renal system. The 
protoplasmic matter of this naked little cell (as well as the waste 
albuminous substances of its food) frequently undergoes chemical 
££ disintegration.” 
II. VORTICELLA. 
The contractile vacuole of Vorticella exhibits, during life, fairly 
regular diastolic and systolic movements. The fluid which it con- 
* The crystals had a splendid green metallic lustre when seen by reflected, 
and a reddish-purple colour by transmitted light. 
