MALE-PRODUCTION IN HYDATINA 535 



other manure scum. The two dishes receiving manure scum as 

 food received also a small amount of water from the Euglena 

 stock (without Euglena), and the dish receiving Euglena as food 

 in spring water received also a small amount of manure solution 

 (without scum). This was done in order to equalize the initial 

 chemical composition of the media in the four dishes, except as it 

 was intentionally made different by manure solution and spring 

 water. After from twenty-four to fort}^ hours the rotifers were 

 removed from their dishes. All offspring hatching from eggs 

 laid in that time were reared to maturity, all four lots alike, in 

 spring water with manure scum as food. 



Comparison of the third and fourth di^'isions of table 6 shows 

 that manure solution reduces the proportion of male-producers by 

 7.31 per cent, but this reduction is more than offset by feeding 

 wd'th Euglena, as in the first division of the table. That is, Eu- 

 glena increases male-production more than manure solution 

 reduces it. If, however, as indicated by experiment 4, over one- 

 third of the total effect of Euglena is due to the oxygen liberated 

 in photosynthesis, then Euglena as food is less powerful in in- 

 creasing male-production than manure solution is in decreasing it. 

 The maximum male-production was obtained, as was to be ex- 

 pected, by using both Euglena and spring w^ater (second division 

 of table 6). The minimum is obtained from manure scum and 

 manure solution together. This minimum is approximately 

 doubled by substituting either spring water for manure solution 

 or Euglena for manure scum. Making both substitutions prac- 

 tically doubles the results of a single substitution. 



Experiment 5. Oxygen versus creatin, Euglena versus creatin. 

 On each of the dates in table 7, three to five rotifers were placed 

 in each of four dishes, the number in each dish being the same on 

 any one day. The four dishes were treated as follows: 1) One 

 lot was immersed in a dilute solution of crude creatin, of the 

 concentration indicated in table 7, and fed Euglena. 2) One dish 

 was filled with a measured quantity of water which had first been 

 saturated with an atmosphere of which 40 per cent was oxygen. 

 Enough of a more concentrated creatin solution w^as added to 

 produce the same final concentration as in the preceding dish. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 26, NO. 3 



