188 THE AMERICAN MONTHLY [July, 



of a living microscopic animal. It maybe easily done. The 

 common Rhizopod, Arcella vulgaris, is abundant everywbere in 

 the surface-ooze of our shallow ponds. Beneath its shell there 

 is frequently formed a bubble of gas, just how it is produced I 

 do not know, but near it, often beside it, may be seen one or 

 more of the animal's contractile vesicles. It is not necessary 

 to prolong the study of the optical action of each of these, to 

 observe that not to discriminate l)etween a gas-bubble and an 

 enclosed drop of a watery liquid, should be impossible. 



It has been my good fortune to observe the actual ejection of 

 the liquid contents from the contractile vesicle of an animalcule. 

 An Infusorian wns encompassed V)}' a cloud of bacteria and of 

 similarly minute bodies or debris, through which, at every con- 

 traction of the vacuole a narrow path was swept with a quick 

 puff, as a passage might be made through the dust by the sud- 

 den blast of a bellows. I studied the effect of the something which 

 issued from that contracting vacuole, and that that something 

 was a liquid I assume ; that it was not a gas-bubble I know. Gas 

 could have been seen to escape, and it would have collected 

 under the cover-glass where it could have been recognized, al- 

 though I am not unmindful of the fact that a bubble has been 

 described as a cancer-cell, and as the microbe of la grippe!!- 



In some Rotifers the channel leading from the contractile 

 vesicle to the external water may be seen and studied at every 

 contraction of the organ. Here the passage is permanent, and 

 although it is closed and invisible except when the liquid is 

 issuing, it is then conspicuous. Yet even in these favorable 

 conditions I have never se^n any effect produced by the ejec- 

 tion, probably because the quantity of liquid expelled is ex- 

 ceedingly small, and because there never happened to be 

 sufficient flocculent matters near enough to the animal's body 

 to be influenced by the slight force of the issuing current. 

 In other Rotifers the vesicle discharges its contents into the 

 lower part of the intestine. 



Dr. Seigfried Czapski of Jena, one of the members of the 

 famous "Carl Zeiss" Optical Company, will be present at the 

 meeting of the American Microscopical Society at Madison, Wis. 

 August 18. He will read an essay and give a demonstration. 



