DEPARTMENT OF EXPERIMENTAL EVOLUTION. 85 



Dr. Banta, has made, with results that support the hypothesis. The experi- 

 ments are as follows : To the water in which the eggs and larvae of Spelerpes 

 bilineatus (which are typically dark brown) are developing have been added 

 certain phenols — substances that are known to inhibit the oxidation induced 

 by tyrosinase. The result has been an almost complete inhibition of pig- 

 ment formation. The larvae, instead of being dark brown, are cream col- 

 ored. The obvious conclusion is : tyrosin only in the body gives recessive 

 white; tyrosin -j- tyrosinase give melanic pigment, that is, dark brown; 

 tyrosin -f- tyrosinase -f- a phenol give dominant white. Further details are 

 given in the following report of Dr. Gortner : 



It was found, if phenols carrying the hydroxyl groups in the ortho or 

 para position are treated with tyrosinase, that oxidation to a color results. 

 If, however, to this mixture a small quantity of a phenol carrying the hy- 

 droxyl in the meta position be added — for example, a small quantity of 

 phloroglucinol, orcinol, or resorcinal — not only does no oxidation of the 

 meta compound occur, but the addition of the meta dihydroxyl phenol in- 

 hibits the action of the tyrosinase on those phenols which are easily oxidized 

 to colors. A study of this reaction showed that the meta dihydroxyl com- 

 pound neither united with the added tyrosin nor was it oxidized itself, but 

 that the reaction in the test-tube was exactly analogous to that of an anti- 

 oxidase, only in this instance the reaction was purely chemical, and not due 

 to an enzyme. The suggestion was made that perhaps it is due to a re- 

 action of this sort that the cause of dominance is due, i. e., that the chromo- 

 gen is changed by some reaction from a para phenol to a meta phenol ; e. g., 

 tyrosin is changed from para hydroxyphenyl a-aminopropionic acid to meta 

 hydroxyphenyl a-aminopropionic acid, thus preventing the black pigment 

 from developing and producing a dominant white condition. It is of es- 

 pecial interest to note that Keeble and Armstrong (Proc. Roy. Soc. B., 85, 

 p. 214), acting on the hypothesis that an anti-enzyme causes the dominant 

 white condition, have recently proven that this hypothesis is correct for 

 material from the Chinese primrose. 



THE ORIGIN AND HEREDITY OF SEX. 



It was early seen that the new methods of studying heredity would throw 

 light on the question of the determination of sex ; and indeed great progress 

 has been made in this and other countries by the combination of the investi- 

 gations of cytologists and breeders. It is now generally recognized that a 

 certain chromosome usually distinguishable from its fellows and which is, 

 essentially, unpaired and so is carried by only half of the progeny of any 

 pair of parents, determines that its bearer shall be of a given sex. The 

 other half are of the opposite sex. This sex-determiner carries with it other 

 characters than merely those that are combined with sex ; and these are the 

 sex-limited or sex-linked characters. The hunt for sex-limited characters 

 has yielded many surprises. In the last few years the Director has studied 

 a case of a sex-limited character in poultry and found that the color of the 

 margin or "lacing" of the neck, or "hackle" feathers, is sex-limited; and 

 that, when crosses are made between races with red and those with white 



