[3] AN INDIRRCT SOURCE OF THE FOOD OF FISHES. 757 



According' to Pritchard the Ghyodorus sphcericiis is the choice food of 

 a species of a i'resh water Nais which he calls Lurco. " So great is the 

 voracity," he says, " of this creature that I have seen a middle-sized one 

 devour seven Lyncei in half an hour." 



Eeferring to the Daphniadcc, our author again observes: "The food 

 of these animals, according to Straus, consists of vegetable matter, and 

 not animal ; but I have found that of two groups placed in separate 

 vessels of clear water, the one having only particles of vegetable mat- 

 ter placed beside theju, while with the other there were also introduced 

 infusorial animalcules, the latter were much stronger, more active, and 

 throve better than the former." 



This appears to be very strong evidence in favor of the animalcular 

 diet of these crustaceans. Other evidence, too, of quite as convincing 

 a character is not wanting. Those who have been in the habit of col- 

 lecting quantities of microscopic material from ponds and ditches have 

 frequently observed very large schools of Entomostraca in such places 

 where the water as a rule is not absolutely stagnant, but where an 

 abundance of duck-weed, fresh-water algse of many kinds, as well as 

 various water plants of the higher orders make a splendid nidus for 

 all kinds of Monads and ciliated and Amoeboid Protozoa. These are the 

 places where Cyclops, Daphnia, and allies flourish inland in fresh water. 

 The writer has also noticed them jparticularly abundant in the wide 

 river flats near the mouth of the Susquehanna at Havre de Grace,where 

 there are large areas many acres in extent which are covered with a 

 luxuriant growth of Potamogeton, Anacharis, and Vallisncria, making a 

 dense mat of delicate stems and leaves upon which countless multi- 

 tudes of Protozoa may fix themselves and abide. If in rowing through 

 such masses of aquatic vegetation one will stop the boat and stir care- 

 fully among the i^lants with the hand over the side, and cautiously 

 watch the result, one will often notice that great numbers of Entomo- 

 straca have been frightened from their leafy retreats. These are the 

 places whex^e young shad ought to be liberated ; in such places they 

 would find an abundance of food at an early period, or as soon as they 

 are fitted to partake of nutriment by swallowing. 



Just as we find the fresh-water forms of Entomostraca take to the 

 shelter of aquatic vegetation at the mouths of rivers, so it appears that 

 many of the marine forms seek i^rotection, and probably food, under 

 cover oX the fronds of marine algte. Here is what their most recent 

 monographer sa> s in relation to this point : " A large number of species 

 haunt almost exclusively the forests of Laminarice which grow on rocky 

 coasts at and below low- water mark ; the fronds of Laminaria saccharina 

 in particular are the favorite abode of many species." (Brady, Monog. 

 Brit. Copep., Introd., i, p. 7.) Again, on page 9, he remarks " The 

 washing of the fronds and roots of Laminarkc, which may be dragged 

 up by means of the hooked grapnels used on many coasts by kelp 

 burners, often afibrds multitudes of Copepoda." 



