may be said, however, that these materially influenced the results 

 obtained. 



The kinds and quantities of the various fish food organisms 

 appearing in the basins varied to some extent with the type of basin 

 and the quality of the polluting substance, and to a larger extent with 

 the temperature of the water and the quantity of polluting substance 

 used per unit area. These variations cannot be discussed in detail 

 until the experiments have been concluded. 



The principal food animals appearing in the basins were the fol- 

 lowing: Micro-crustacea, especially the little cladoceran, Scapho- 

 leberis, and the copepods, Cyclops and Canthocamptus; mosquitoes of 

 two species ; "blood worms" of the genus Chironomus; rat-tail mag- 

 gots, larvse of the family Syrphidae ; the common pollution worm, 

 Tubifex, and mayflies of the genus Callibaetis. 



Of these the mosquitoes, syrphid flies and mayflies were attracted 

 to the basins for egg-laying by the odors of pollution. The micro- 

 crustacea and pollution worms were probably introduced with the 

 water and finding conditions suitable, multiplied to an enormous de- 

 gree. 



MOSQUITO LARVAE 



Considering the total amount of fish food produced, the mosquito 

 larvae were by far the most important. The adults began laying eggs 

 the first week in July (1920 and 1921) and continued to do so 

 throughout the summer. In 1920 the larvse were abundant late in 

 September. 



Of the two wastes, sour skim milk and whey, the former induced 

 egg-laying in the shortest time and with the smallest dosage. Up to 

 the present time the dosage giving the most promising results at 

 Ithaca, N. Y., is as follows : 



One pint of skim milk for every 10 cubic feet of water content 

 in pond, poured in every other day for 5 days, this followed by a 

 resting period of 4 to 6 days. In order to have a continuous supply 

 of larvae, the procedure is repeated after each resting period. The 

 mean daily water temperature for this dosage should be approxi- 

 mately 80° F. If the temperature averages lower the period of de- 

 velopment will be longer ; if higher, it will be somewhat shorter. 



In a wooden hatching trough treated in this manner there were 

 produced 2 egg masses the second day, 6 masses on the third day. 111 

 on the fourth day, and an incalculable number on the fifth day, each 

 mass consisting of a great many eggs. From the eighth to the 

 eleventh day the basin was a wriggling mass of larvae, many of them 

 ready to pupate, and thus sufficiently large to be fed to trout or bass. 



77 



