266 CHARLES R. STOCKARD 



Stock ARD, C. R. 1913 b An experimental study of the position of the optic 

 anlage in Amblystoma punctatum, with a discussion of certain eye 

 defects. Am. Jour. Anat., vol. 15, p. 253. 

 ~ — 1914 A study of further generations of mammals from ancestors 

 treated with alcohol. Proc. Soc. Exp. Biol, and Med., vol. 11, p. 136. 

 1919 Developmental rate and the formation of embryonic structures. 

 Proc. Soc. Exp. Biol, and Med., vol. 16, p. 93. 



Stockard, C. R., and Papanicilaott, G. N. 1918 Further studies on the modi- 

 fication of the germ-cells in mammals: the effect of alcohol on treated 

 guinea-pigs and their descendants. Jour. Exp. Zool., vol. 26, p. 119. 



Tannretjther, G. W. 1919 Partial and complete duplicity in chick embryos. 

 Anat. Rec, vol. 16, no. 6. 



Thorndike, E. L. 1905 Measurements of twins. Arch. Phil., Psych, and Sci. 

 Methods, vol. 13, no. 3. 



Vejdovsky, Fr. 1888-1892 Entwicklungsgeschichtliche Untersuchungen. 2 

 vols, text and atlas, Prag. 



von Jhering, H. 1885 Ueber die Fortpflanzung der Giirteltiere. Sitzungsb. 

 d. konigl. Akad. d. Wiss., Bd. 47, S. 105. 



Wilder, H. H. 1904 Duplicate twins and double monsters. Am. Jour. Anat., 

 vol. 3. 



1908 The morphology of cogmobia; speculations concerning the sig- 

 nificance of certain types of monsters. Ibid., vol. 8. 



Wilson, E. B. 1893 Amphioxus and the mosaic theory of development. Jour. 

 Morph., vol. 8, p. 604. 



1904 Experimental studies in germinal localization. I. The germ- 

 regions in the egg of Dentalium. Jour. Exp. Zool., vol. 1, p. 1. 



Windle, B. C. a. 1895 On double malformations amongst fishes. Proc. Zool. 

 Soc. London, pt. 3. 



Zoja, R. 1895-1896 SuUo sviluppo dei blastomeri isolati delle uova di alcune 

 Meduse. Arch. Entw.-mech., Bd. 1, u. 2. 



PLATE 1 



explanation of figures 



A series of young trout that started development with a slightly insufficient 

 supply of oxygen. The series begins with an ordinary single individual and 

 passes through increasing degrees of anterior duplicity, shown in the two upper 

 rows. It then continues with specimens showing step after step of completely 

 formed double bodies and tails and finally ends with perfectly formed identical 

 twins, in which both members of the pair are equally as large and perfect in 

 structure as is the first single individual. 



The photographs were all made at one magnification and show as nearly as 

 possible the dorsal aspect of each specimen. On careful examination it will be 

 found that in every specimen the two components are practically identical in size, 

 and when the anterior halves are considered all heads are found to be normal in 

 structure. 



