128 WINIFRED HUGHES. 



stimulus may be supposed to have been caused by the loss of 

 blood following the establishment of a common circulation 

 between the twins. This took place after differentiation of the 

 external genitalia, and consequently these are normal in structure. 

 Later developments, including complete differentiation of the 

 genital ducts, degeneration of the mesonephroi, growth and 

 descent of the testes, have been affected, and these therefore show 

 evidence of irregular and uncontrolled growth. 



These are only suggestions, however. More material is re- 

 quired to clear up these doubtful points, and it is hoped that 

 further investigation will determine more definitely the extent to 

 which intra-uterine conditions are responsible for the production 

 of sexual abnormalities in the pig. 



BIBLIOGRAPHY. 

 Allen, B. M. 



'03 The Embryonic Development of the Ovary and Testis of the Mammals. 



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Br. Journ. Exp. Biol., Vol. II.. No. 2. 

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'23 The Interstitial Cells of the Gonads of Cattle with Especial Reference to 

 their Embryonic Development and Significance. Amer. Journ. Anat., 

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 Bissonnette, T. H. 



'24 The Development of the Reproductive Ducts and Canals in the Free- 

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Life of Cattle. Journ. Exp. Zool., Vol. 23. 



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