246 PHYSIOLOGY OF THE INVERTEBRATA. 



secretory organs as we pass from the lower to the higher 

 forms of the Invertebrata. 



The Protozoa. 



The author* has shown that the contractile or pulsating 

 vacuole of the Protozoa performs the function of a true 

 kidney, or, in other words, its secretion is capable of yielding 

 microscopic crystals of uric acid. 



Three organisms were used in the author's experiments — 

 namely, Amceba, Vorticella, and Paramoscmm. 



(i) Amceba. — By observing a number of these organisms 

 under the higher powers of the microscope,! there is seen, 

 within the structure of each, a small cavity or vacuole filled 

 at certain times with a transparent fluid. There is little 

 doubt that the fluid which collects in the vacuole is drawn 

 from the surrounding protoplasmic substance, and is returned 

 to it, or forced out to the exterior on the contraction of the 

 walls of the vacuole. 



The author has shown in his paper, " Further Researches 

 on the Physiology of the Invertebrataj" \ that the five 

 pouches of the Asteridea also perform the function of 

 kidneys (i.e., the digestive apparatus performs a dual 

 function) ; and whatever may be the multitudinous func- 

 tions of the Protozoan contractile vacuoles, one thing is 

 certain, that they excrete periodically a waste nitrogenous 

 substance. This nitrogenous substance was proved to be 

 uric acid. 



A number of Amosbm were placed on a microscopic 

 slide and covered by a thin cover-glass. Alcohol was run 

 in between the slide and cover-glass, so as to Mil 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 



* Proceedings of Royal Society of Mdinhurgh, vol. i6, p. 131. 



t Zeiss's E and oc. v ; F and oc. iv and v. 



:f Proceedings of Boyal Society of London, vol. 44, p. 325. 



