328 Aquatic Societies 



Cayuga is placed in a beaker, the Bosminas begin 

 to break through one by one, and soon are gathered in a 

 little floating company in the center. 



Scapholeberis (fig. 192), however, appears to be 

 especially fitted to take advantage of the surface film. 

 It is able to maintain a proper position at the surface : 

 it possesses specialized bristles for breaking the film and 

 laying hold upon it; its ventral (uppermost) margin 

 is straightened and extended posteriorly in a long 

 spine; as much contact may be had as is needed. 

 Suspended beneath the surface, where algae from below 

 and pollen from the air accumulate, Scapholeberis 



Fig. 192. Scapholeberis mucronata, 

 suspended beneath the surface film. 

 (After Scourfield.) 



rows placidly about, foraging ; or it is borne along by the 

 towing of air currents acting on the surface water — a 

 sort of submarine sailing. 



Scapholeberis is unique among water-fleas in this 

 habit. There is also an Ostracod, Notodromas, of 

 similar habit ; and it is worthy of note that both these 

 creatures have blackish markings on the ventral edges 

 of the valves and are pale dorsally. As in the sloths 

 which climb inverted in trees, the usual coloration of the 

 body is reversed with reversal of position. 



Then there are some little creatures that take advan- 

 tage of the tenacity of the surface film to cover them- 

 selves with it as with a veil. Copepods, ostracods, 

 rotifers and what not, climb up the surface of emergent 

 stems, pushing a film of water ahead until they are well 

 above the general surface level, where they rest and 



