STRUCTURE AND DEVELOPMENTAL RATE 247 



9. CONTINUITY OF THE SERIES FROM MONSTRA IN DEFECTU 



THROUGH THE SINGLE NORMAL INDIVIDUALS TO MONSTRA 



IN EXCESSU AND FINALLY IDENTICAL TWINS 



It has long been recognized that certain types of monsters ex- 

 hibit their characteristic defect to varying degrees. The Cyclo- 

 pean series, for example, may present individuals not only with 

 a single median eye, but with a bilaterally wide eye, hour-glass 

 eyes, and finally closely approximated separate eyes. The series 

 of diplopagi likewise exhibit all degrees of doubleness, as illus- 

 trated in plates 1 to 4. 



In studying monsters belonging to these groups. Wilder ('08) 

 went a step further and called attention to the fact that the so- 

 called series of defective monsters passed by degrees up to the nor- 

 mal individual and continued from there through the excessive 

 series on to identical twins. He was impressed by the 'orderly 

 development' of the members in such a series and termed these 

 individuals 'Cosmobia.' The treatment of the series as variations 

 about the normal as a standard was a most important advance in 

 an analysis of their structural conditions. Wilder further empha- 

 sized the important fact that monstra in defectu and monstra in 

 excessu are both due to the same kind of cause and should be 

 considered together in any general treatment of the subject, 

 especially concerning cause. 



However, after enunciating this clear arrangement of the prob- 

 lem. Wilder was entirely misled in his interpretation of the cause 

 of these individual anomaUes. The fact of their 'orderly' and 

 symmetrical structure, and the further evident fact that normally 

 formed identical twins represent the termination of the diplopage 

 series, led him to consider all such forms as due to a definite germ- 

 inal variation. It seemed to him more probable that orderly 

 deviations from the normal would arise in the germ-plasm than 

 that they should occur as a result of some modification during 

 individual development. The burden of evidence, however, is 

 unfortunately against such a proposition, and weighs decidedly 

 more at the present moment than when Wilder published his 

 account. 



