440 Harris Hawthorne Wilder 



half will regenerate a left girdle-half with the associated limb, and the 

 separated left half will regenerate a right. In the case of duplicate 

 twins the splitting divides the entire body into its two bilateral halves 

 and each half regenerates the lacking half. This theor}^, he claims, 

 is not at variance with any of my investigations concerning snch twins, 

 and he even finds that he can employ my diagram showing the series 

 of double monsters leading to duplicate twins^^ to explain the theory he 

 presents. 



If one wished to seriously oppose this school of superregenerationists 

 he could do it most properly by pointing out, first, that no instance of 

 these frightful fetal injuries has ever been observed, and, second, that, 

 on the other hand many embryonic stages of genuine double monsters 

 are known, including such very early ones as those of Kaestxer, and 

 yet, even in these, there is no trace of any fetal calamity. Surely, if 

 such monsters were formed by any regenerative process an embryo would 

 occasionally be found in which the process is still incomplete, but as 

 a matter of fact, the earlier the embryo so much the more symmetrical 

 and typical are the two components, while inequalities in the compo- 

 nents make their appearance later on in development. This final argu- 

 ment shows the great need of the study of teratembryology, especially 

 that of types belonging to the various cosmobiotic series. 



^^Duplicate twins and Double Monsters, Amer. .Journal of Anatomy, Vol. 

 III. No. 4, 1904, PI. A. 



