THE CATALYST ENTELECHY IN DIFFERENTIATION 203 



Considering now the amphibian sex duct systems, the Wolffian 

 duct, with male potentialities, arises as the pronephric or segmental 

 duct on each side of the body. The Mullerian duct, with female 

 potentialities, generally originates independently from the epithelium 

 of the coelom. These two form all the later ducts, and both of them 

 appear in every organism; but the particular sex hormone poured into 

 the blood stream determines which of the two systems will persist 

 and develop. The non-developing system normally degenerates into 

 a vestigial structure; but we can understand how in abnormal cases 

 there may develop intersexes or hermaphrodites. The various second- 

 ary sex characters (external genitalia, accessory sex glands; wattles, 

 spurs and combs of fowl) are all controlled by the sex hormones. 



Sex reversal is known to occur spontaneously (Pflugerian herma- 

 phroditism), and as before noted can be artificially induced. Oysters 

 are usually male when young, but become female as they grow older. 

 The Florida silver palm also changes sex. 45 With the sex substances 

 there seems to be a balance, controlled in part by temperature and 

 differential diffusibility. If two frog larvae of opposite sexes are 

 grafted side by side and develop toward maturity, the male medulla 

 will suppress the cortex of only the nearer ovary. But if the larvae 

 are grafted in tandem, no effect is noticed, the diffusion path being too 

 long. With urodeles (newts) side-by-side grafting suppresses both 

 ovaries of the female partner. The effect may be quantitative; for if 

 the female of a large species is grafted to the male of a small species, 

 the ovaries suppress the testes. High temperature and over-ripeness 

 of eggs favor maleness, e.g., the medulla over the cortex. By grafting 

 an ovary into a cool spot (ear or scrotum), involuted sex organs of 

 castrated mice have been restored to normal, apparently by the small 

 amount of androgen supplied by the ovary; but grafting onto the 

 warmer abdomen was without effect. 40 



By injections of oil solutions of estrone into the allantoic cavity 

 of birds' eggs on the fourth day of incubation, V. Danschakova and 

 J. Massavicius 47 completely feminized the embryos of genetic male 

 birds. But the introduction of testosterone proprionate to effect 

 masculinization was lethal in birds, though with guinea-pigs the free- 

 martin effect was produced, the male hormone suppressing feminiza- 

 tion. 



The case of the gephyrean worm Bonellia is fantastic. From the 

 body of the female, about the size of a walnut, there projects a yard- 

 long probosis which serves to collect the nutrient-containing mud. 

 The tiny male, less than 3 millimeters in length, lives as a commensal 

 in the female's intestine and uterus. Less than one percent of the 

 larvae spontaneously develop into males. Ninety-nine percent of the 

 free-swimming larvae will become females unless they happen to 



