122 



CARNEGIE INSTITUTION OF WASHINGTON. 

 Table 5. 



Where acid was added to the solution from Pond I, "all male" 

 broods were produced ; when untreated or with alkaU added to this so- 

 lution ''all female" broods were produced. Just the reverse was 

 true with the food solution from Pond II ; the addition of alkali pro- 

 ducing "all male" broods in 2 out of 3 cases and the addition of acid 

 resulting in "all female" broods. There was 1 "all male" brood in the 

 untreated food from Pond II. These are not completely differential 

 results, but they are suggestive and, considered in connection with other 

 experiments, this significance becomes unmistakable. Other sets of 

 experiments similar to the two mentioned above resulted similarly. 

 The experimental evidence may be said to have considerable weight. 



The experiments were not all equally successful, however, and some 

 produced no significant results at all. This lack of uniformity in the 

 experimental results is attributed to variable factors in the culture- 

 water. While the culture material is more or less the same at all 

 times, it will readily be recognized that at different times considerable 

 differences occur in the constituents of an outdoor pond-water in 

 which Uve many small and larger organisms. So far as the relative 

 degree of alkalinity is concerned, it apparently operates to influence 

 the sex of the daphnids through some other factor or factors; hence 

 it is a controlling influence apparently working through an unknown 

 environmental factor. Its control of sex is none the less significant, 

 however. (A standard culture medium. Dr. Banta suggests, would 

 afford excellent opportunity to attain complete control of sex.) 



Production of epMppia. — Strange as it may seem, the production of 

 ephippia does not ordinarily occur in the laboratory simultaneously 

 with the production of males, and frequently males and ephippia do 

 not coexist in outdoor ponds. There is evidence that the production 

 of ephippia, too, is controlled by environmental factors. 



Origin of a second sex-intergrade strain. — During the occurrence of 

 males in the spring, sex-intergrades were produced, in Dr. Banta's 

 cultures, by several mothers in one of the strains of Daphnia longispina. 

 These were mothers which also produced normal males. Propagation 

 from these sex-intergrades has resulted in the establishment of a strain 

 of sex-intergrades of D. longispina. This strain produces, in addition 

 to normal females, sex-intergrades in every generation. 



