gill] the umbras 301 



minnow" (Umbra limi) of Illinois, "vegetable food amounted to 

 forty percent, chiefly Wolffia " (an aquatic lemnaceous plant), and '' a 

 considerable quantity of unicellular alg^e was also taken by one ; 

 mollusks, eaten by two, were reckoned at five percent, all Pliysa ; 

 insects drop to fourteen percent, chiefly undetermined larvae. No 

 terrestrial forms were recognized. Corresponding to the greater 

 development of the gill-rakers, we find the Entomostraca assuming 

 greater importance in the food. These were reckoned at ten percent ; 

 three percent additional consisting of Crangonyx gracilis'' a small 

 amphipod crustacean. Five specimens of the Umbra limi obtained 

 from a pond, " covered in September with a film of Wolffia and 

 other vegetation," yielded to the dissector stomach contents consist- 

 ing of sixty percent of the Wolffia; of the remainder " about one- 

 fourth consisting of Entomostraca " and the rest of " unrecognized 

 insects." 



In captivity they will readily take small shreds of meat as well as 

 their natural food. " When kept in aquaria they will devour any 

 reasonable number of flies ofifered them, and undertake without hesi- 

 tation to swallow earth-worms as large as themselves. Once they 

 take hold of a worm, they never let go, but at least secure that 

 portion of the animal between their jaws. Not only do they allow 

 themselves to be fed, but they will leap above the water to seize 

 any tempting morsel held above them." Long ago (1842) Zadock 

 Thompson was struck by their power of accommodating themselves 

 to dififerent conditions and declared that they can " live longer than 

 most fishes without water. During droughts, as the waters subside 

 and recede from the caves, they have the power, by a springing 

 motion, of transporting themselves from one little puddle to another. 

 They also have the power of partially burying themselves and living 

 in the mud and among the moist grass-roots, after the other small 

 fishes associated with them are all dead for the want of water. In 

 these situations vast numbers of them are devoured by birds, musk- 

 rats, and foxes." 



This power of adaptation enables them to find a winter-home with 

 the least waste of energy and loss of life, and to hibernate in the mud. 

 The mud was found by Abbott in midwinter to be of " the consistence 

 of cheese, though, of course, it was less firm when the fish 

 entered it, weeks before." As far as he was " able to determine the 

 fish had burrowed tail-foremost to a depth of from four to nine 

 inches." In every instance " the tail was deeper in the mud than the 

 head, the position varying from nearly horizontal to almost or quite 

 perpendicular." 



