150 Phylum Plathelminthes 



such Copepoda as Cyclops [see p. 227]. Of aerating value are a few 

 branches of Elodea or a small mass of Spirogyra or both. In this culture 

 the Microstoma may then be placed. Microstoma living in the presence 

 of water plants are more active and of larger size than those living in 

 control cultures without these plants. In such a culture the animals may 

 be expected to thrive indefinitely, if at intervals some of the detritus be 

 drawn off with a clean pipette and replaced with fresh water, and if 

 food be supplied regularly. 



The food which serves best, in my experience, is the annelid Dero 

 [see p. 143]. Every two or three days the Microstoma should be fed 

 small, freshly cut sections. Enough should be placed in the culture to 

 supply each Microstomum with three or four pieces, for the animals 

 eat voraciously when in a healthy condition. The Dero may be cut 

 easily by means of two small needles used in criss-cross fashion. The 

 pieces should not exceed the size of the Microstoma and must be freshly 

 cut. If the food has been prepared for an hour or more before feeding, 

 the wounded surfaces of the annelid heal, thus cutting off the flow of 

 the fluid by which the Microstoma sense the presence of the food most 

 readily. In such case, or whenever the Microstoma seem insensible to 

 the presence of food, they may find and eat it if several pieces are freshly 

 cut in the culture. 



Other conditions being favorable to growth, the size of the Microstoma 

 is directly related to the amount of food consumed. Animals with six 

 zooids often occur in vigorous cultures. On the other hand I have had 

 Microstoma live in favorable cultures for two weeks without feeding. 

 Under such conditions they become progressively smaller until they die 

 from starvation. 



The foods eaten by Microstomum under my observation, listed in 

 order of preference, are: Dero, Hydra, liver (tadpole and mammalian), 

 Cypris, Daphnia, Cyclops, Difflugia, Pristina, egg yolk, Stentor, desmids, 

 and Nematodes. 



Hydra, as food for Microstomum, deserves special mention. It seems 

 to act as a tonic for animals which are not in good condition as evi- 

 denced by their lack of response to food. If, as sometimes occurs, the 

 Microstoma cannot sense food, or refuse it, fragments of hydra, fed in 

 the same way as the annelids, will rejuvenate them. 



Reference 

 For the culture of Microstomum see also p. 136. 



