THE ZOOCHLORELUE OF FRONTONIA LEUCAS. 



81 



Three living specimens were found in one, and five in the other. 

 On September 22 duplicate cultures were started with similar 

 results. 



September 30, collections of Frontonia harboring innumerable 

 zoochlorellae were made and change from the original culture 

 medium to fresh spring water was made gradually by drawing 

 off a part of the medium daily and replacing it with fresh spring 

 water. Under these conditions it was observed that within 

 forty days the zoochlorellae had completely disappeared, while 

 the ciliates showed no signs of death. 



Slides made at intervals extending over the forty-day period 

 corroborate these observations (Fig. i). Various stains and 

 fixatives were used in making the slides, but the most satisfactory 

 results were obtained from Looper's fixative l and iron hsemo- 

 toxlyn. 



From these observations it is evident that Frontonia may be 

 freed from their zoochlorellae by a gradual transference from 

 their natural habitat to a medium of fresh spring water. 



INCREASE IN NUMBER OF ZOOCHLORELL.E IN HOST. 

 In a collection made from a large semi-stagnant pond, July 2, 

 1925, Frontonia with very few zoochlorellae were abundant. 



FIG. 2. Typical specimen from a collection in which the Frontonia contained but 



few zoochlorellae. 



Slides from the collection showed the average specimen to 

 contain from fifty to one hundred zoochlorellae (Fig. 2). The 



1 Make a thin smear of Mayer's egg albumen the size of a dime on a clean slide. 

 Place the ciliates to be fixed on the smear in a drop of water just large enough to 

 make a thin layer over the albumen. Invert the slide over the mouth of a small 

 bottle containing a mixture of equal parts of 95 per cent, alcohol, glacial acetic 

 acid and formalin. Let the slide remain in this position 30 seconds to a minute. 

 Remove the slide and slant it back and forth until the film of water has almost 

 disappeared. Wash gently in water and stain. 



