1893.] MICROSCOPICAL JOURNAL. 83 



The attempt to establish the presence of uric acid crystals in 

 the vesicle gave very unsatisfactory results. I am not inclined to 

 the belief that the function of the vesicle is essentially excretory. 

 I believe the prime function is respiratory and circulatory. It is 

 to facilitate the interchange of CO., in the interior and O in the 

 surrounding water. During a diastole an interchange of gases 

 takes place by osmosis. By means of the canals and Vorhofe, 

 CO.,, or at least a gas highly surcharged with CO^ , is conducted 

 to the vesicle, where some of the CO., is exchanged for O taken 

 from the water. A deficiency of O in the protoplasm, probably 

 acting as a stimulus, causes a contraction and forces the gas, 

 now containing an excess of O, through the Vorhofe and canals 

 into the general system. The vesicles are always located in such 

 a position as to favor the supply of oxygenated water. In a free 

 swimming organism, like the Paramecium^ it does not matter so 

 much where thev are located, as their continuous motion brings 

 them in contact with oxvgenated water. In fixed organisms, 

 like Vorticella, the vesicle is located near the oesophagus, where 

 there is a continuous current of water kept up by the cilia. 



When a circulatory and respiratory function is mentioned it 

 must not be understood as at all similar to respiration and circu- 

 ation in man Let there be no misunderstanding on that score. 



Summary. 



1 . The two contractile vesicles of Parameciu7?i aurelia con- 

 tract alternately with great regularity. 



2. The essential parts of a contractile vesicle are the vesicle, 

 Vorhdfe, and canals. 



3. There are no visible openings connecting the vesicle with 

 the exterior. 



4. There is no visible ejection of any substance from the 

 vesicle. 



5. The function of the contractile vesicle is probably respiratory 

 and circulatory. 



The contractile vesicle probably has no excretory function. 



The Spiracles of the Click-heetle. 



By EWARD gray, M. D. 



SANTA CRUZ, CAL. 



In a previous article upon this subject, which was published in 

 this periodical for November, 1S91, the writer put the ques- 

 tion, who could aid him in obtaining specimens of the cylin 

 drical grub of the click-beetle, sometimes called the wire- 

 worm. During the year 1S93 no response was received, but 

 within the past fortnight a well-prepared slide of this object has 

 reached the writer from Mr. F. Dienelt. This slide is superior 

 to that which called forth the article named, and estal)lishes the 



