riddle: control of sex ratio 349 



mal. It is highly probable, therefore, that precisely that time 

 relation which leads to an excess of males in cattle is preceded 

 or accompanied by an increased hydration of the ovum. In 

 mammals therefore there is some evidence that a shift of the 

 metabolic level — as indicated by one partly known differential 

 — is associated with the observed changes in the sex-ratio of the 

 germs which are thus modified. Further, in the adult of one 

 mammal — man — two of the three sex-differentials have been 

 definitely demonstrated. These results for both the egg and 

 adult stages of the mammal are at every point in complete agree- 

 ment with our data for both the egg and adult stages of the 

 bird. 



How now do the controlled sex ratios obtained in the frogs and 

 toads appear in the light of the sex differentials of our diagram? 

 Clearly the data given in Table 11 arrange themselves in per- 

 fect agreement with the metabolic differentials which obtain in 

 birds and mammals. The data of that table eliminate "de- 

 layed fertilization" as such as being a factor and show that the 

 altered sex ratios correspond with increase or decrease of water 

 as the sole known differential. 



We next give a moment's consideration to an adult stage in 

 which a change in metabolism was observed in connection with 

 sexual changes. In the spider-crabs Geoffrey Smith ('11) 

 showed that both the blood and the liver of the adult male crabs 

 contain less fat than do the blood and liver of the females. 

 Here once more the facts concerning one of the sex-differentials 

 is known and is in complete accord with all the preceding cases. 

 In these spider-crabs, known to be sometimes castrated by para- 

 sites, Smith and Robson were able to show, moreover, that the 

 parasitized male crabs, which under these conditions gradually 

 assume several female morphological characteristics, are also found 

 to have assumed the type of fat metabolism which characterizes the 

 normal female crab. How much these facts contribute to, and 

 how completely they adjust themselves to, our own general 

 theory, will be realized only after a moment's reflection. Re- 

 cently Kornhauser ('16) has found some of these conditions also 

 in Thelia. 



