263] TUKBELLARIA FROM THE MISSISSIPPI BASIN—HIGLEY 69 



time was taking food in the same manner as adults. The color was that of 

 the adult except that it was very much Hgher. The size was 0.75 by 0.6 mm. 

 to 0.86 by 0.65 mm. The animal was a little more slender than the adult. 



LIFE HABITS 



The surroundings and immediate environment of these forms are much 

 the same as those for other rhabdocoel species. Strongylostoma rosaceum 

 lives in ponds containing a rather large amount of green algae and perhaps 

 some few other water plants, with usually a muddy bottom more or less deeply 

 covered with leaves, sticks, and organic debris. The other animal forms 

 common in the ponds are such as will be found in very many other representa- 

 tive puddles. About twelve species of Cladocera, fifty rotifers, about a hun- 

 dred protozoa, ten or twelve aquatic oligochaetes, besides very many insect 

 larvae also inhabit these ponds. 



Several environmental factors are of some detailed significance, perhaps 

 the most vital of which is the water condition. The oxygen content seems to 

 have Httle direct relation to the life processes, as the animal carries on its 

 existence with seemingly equal ease in the clearest, freshest water, containing 

 a high percentage of oxygen or in water heavily laden with carbon dioxide. 

 The pond water altho constantly kept in motion by a steady stream running 

 thru it, was often, especially near the bottom, very thick and muddy. Some- 

 times thoroughly clogged with algal masses so that many parts were dark, 

 it also supported an extraordinarily large population of animal species. Owing 

 to a lack of balance a number of times in the aquarium jars, the water became 

 very stale so that there was a great amount of bacterial growth and much of 

 the algae died. Such conditions were, of course, fatal to a great deal of the 

 animal life and in time would do away with those of the flatworm type also. 

 These, however, seemed to withstand such adverse conditions longer than 

 most of the others. The water temperature varied within very wide limits 

 without causing any great difference in life processes except, perhaps, in the 

 case of the reproductive organs. The summer temperature is high and when 

 standing in a sunny window, the aquarium jars were often warm. Here the 

 animals thrived, being more active in the warmer water. On the other hand, 

 the reproductive season comes during the early winter months and that it is 

 in the coldest months that the young generation starts its life independently, 

 is a fact probably to be correlated with the low temperature. Thus the vegeta- 

 tive activity seems greater in warm conditions while the reproductive organs 

 function alone during the winter. However, the life-cycle seems to be com- 

 pleted very soon after the eggs are laid, the individuals not existing thru all 

 seasons. This may be due solely to the depletion of organic strength or, as 

 seems possible, to the fact that the severest and prolonged cold comes at a 

 time when the animals are weakened and unable to withstand such rigorous 

 changes. The reaction to light is positive but neither precise nor immediate. 

 When placed in watch glasses of water, lighted from one side, the individuals 



