S36 EVOLUTION, HEREDITY, EUGENICS 



Newman, H. H. 1923. The Physiology of Twinning. Chicago Press. 

 Newman, H. H. 1931- The finger prints of twins. Jour, of Genetics, 



vol. 22, no. 3. 

 Newman, H. H. 1931- Palm print patterns in twins. Jour, of Her., 



vol. 22, no. 2, pp. 41-48. 

 Patterson, J. T. 1927. Polyembryony in animals. Qu. Rev. of Biol., 



vol. 2, no. 3, pp. 199-426. 



Hermaphroditism and the Free-Martin. — Sex intergrades or 

 hermaphrodites are found in many of the Invertebrate Phyla, and in 

 all classes of vertebrates. Crew has described an instance of sex 

 reversal in a frog which changed from a normally functioning female 

 to a male that was capable of fertilizing eggs and had 774 offspring, 

 all females. Crew also described a fowl that changed from a fertile 

 female to a fertile male. Riddle reported sex reversal in the pigeon. 



Intersexuality in the lower mammals is quite common. It has 

 been described in cattle, sheep, pigs, goats and rabbits. Some of 

 the most interesting studies have developed in connection with 

 "free-martins." The "free-mariin" known for years to stock 

 breeders, is an incomplete female born co-twin with a male. 



The chorionic membranes of the two embryos are fused together 

 and the blood vessels anastomosed so as to produce a common 

 circulation. The testis of the bull calf develops more rapidly than 

 the ovary and its embryonic interstitial gland supposedly exercises a 

 masculinizing influence. 



Tandler and Keller (1916) and Lillie (1916 and 1917) independ- 

 ently showed that in the free-martin the twins come from two eggs. 

 They concluded that the free-martin is a female whose gonads have 

 been transformed into a testis-like organ by male hormones from 

 her twin brother. Willier has said, " the primordium of each male 

 structure developed in the free-martin gonad is present in the ovary 

 at the time of sex differentiation." Bissonnette has shown that the 

 free-martin began as a female and developed as such for some time, 

 then became modified in the male direction internally, though almost 

 never externally. 



References on Free-Martins 



Bissonnette, T. H. 1924. The development of the reproductive ducts 

 and canals in the free-martin with comparison of the normal. 

 Am. Jour, of Anat., vol. 22, no. 2, pp. 267-345. 



