670 GARY N. CALKINS 



nuclei are absent. The contractile vacuole is terminal and is 

 usually accompanied by one or more fluid vacuoles. Very 

 often the entire posterior part is drawn out into a fine vacuole- 

 filled thread which gives to the organism a striking resemblance 

 to Spirostomum teres. Not infrequently this entire poste- 

 rior vacuole-bearing part is pinched off, leaving the remainder 

 of the body with a decidedly truncate base, recalling Miiller's 

 Trichoda aurantiaca (fig. 9) . 



Habitat and food 



Miiller found his Trichoda ignita among Lemna in fresh 

 water, Bory found Ypsistoma on Oscillaria, and Ehrenberg, 

 Bursaria lateritia on conferva. Stein also speaks of it in con- 

 nection with filaments of algae. Biitschli speaks of its food 

 only in a general way as 'Nahrung fein,' 



I ^found a large number of specimens among decaying algae 

 in pond water at Woods Hole, Massachusetts, in July, 1911. 

 One individual was isolated in filtered water from the same 

 source, and experiments were immediately begun to deter- 

 mine the best medium for its continued cultivation. Without 

 going into details in regard to these experiments it will suffice 

 here to say that the most satisfactory medium was found to 

 be pond water with about 50 per cent of twenty-four hour hay 

 infusion. On this medium which is renewed daily, the descend- 

 ants of the originally isolated specimen have divided 224 times up 

 to the present day (June 12), or less than one division per day on 

 the average. All specimens have been colorless for the last 

 five months. The food, therefore, appears to be bacteria of 

 ordinary hay infusions, the best results being obtained with a 

 relatively small number of bacteria, or in other words, with as 

 little as possible of the bacterial waste matters. 



Later in the summer (September) an effort was made to find 

 other wild specimens from the same source as the original but 

 without success, so that the observations here recorded were 

 made on material derived from the original specimen isolated 

 on the 20th of July. The full history of this culture, to- 



