PHYSIOLOGY OF THE INVERTEBRATA. 247 



warmed, and finally, ammonia introduced between the slide 

 and cover-glass. In a few minutes prismatic crystals of 

 murexide,* of a beautiful reddish-purple colour, made their 

 appearance. After the addition of alcohol (as already stated), 

 minute flakes were 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 were 

 minuie crystals of uric acid. 



It may be stated that there are times when the fluid of the 

 contractile vacuoles does not contain the least trace of uric 

 acid. These vacuoles perform more than one function, one 

 of these being that of an internal respiratory apparatus (see 

 last chapter) ; and now we find the same organ performing 

 the function of a kidney. There is little doubt that the 

 contractile vacuole of Amozba is the primitive representative 

 of a series of organs which become gradually differentiated in 

 the higher forms of the Invertebrata. 



(2) Vorticella. — The contractile vacuole of Vorticella ex- 

 hibits during life fairly regular diastolic and systolic move- 

 ments. The fluid which it contains is drawn from the 

 surrounding protoplasmic matter, and is ultimately forced 

 by the contraction of its walls towards the periphery of the 

 bell, and finally ejected into the water in which the organism 

 lives. The contractile vacuole of Vorticella performs the 

 function of a true kidney. Its fluid contents yield micro- 

 scopic crystals of murexide and uric acid when submitted to 

 the same chemico-microscopical reactions as those just de- 

 scribed. 



(3) Paramcecium. — The contractile vacuoles of this organism 

 are situated in the ectosarc almost at each end of the long 

 axis of the body. These cavities are filled with a transparent 

 fiuid. During the systole fine radiating canals are produced, 

 which probably communicate with the exterior. The con- 

 tractile vacuoles of Paramcecium are at times the renal 



* The crystals had a green metallic lustre when seen by reflected, and a 

 reddish-purple colour by transmitted light. 



