528 E. I. WERBER 



logical discovery of Child's as an important key to the under- 

 standing of the nature of chemical defects, and on the .assump- 

 tion of fusion of two originally separate early optic anlagen as 

 underlying the formation of synophthalmic and cyclopean mon- 

 strosities. 



2. The defect-theory of teratophthahnia 



When Fundulus eggs are subjected to the influence of toxic 

 solutions of a perceptibly injurious (but not lethal) concen- 

 tration for a certain (not lethal) length of time, it can usually 

 be found that among the many monstrous embryos which will 

 develop, a certain rather large number will exhibit deformities 

 of the eyes, while other parts of their bodies may appear not, 

 or only very slightly, to deviate from the norm. In such 

 embryos the eye deformities are often the most, if not the only, 

 striking ones. Since the entire eggs were subjected to the influ- 

 ence of the toxic solution, it appears rather puzzling that the 

 developmental product of the egg should show the effect of the 

 treatment only at such a locally restricted area. In experiments 

 in which mechanical methods (such as pricking — Lewis '09, or 

 constriction — Spemann '04) are employed the local deformation 

 can readily be accounted for by the locally restricted lesion 

 which has been caused mechanically. In the chemical experi- 

 ment, however, the treatment is not restricted to a part of the 

 egg, and yet the effect is so often a restricted one. How can 

 this be accounted for? 



There is, so far as I am aware, only one known fact, which will 

 account for this interesting phenomenon. This is Child's impor- 

 tant discovery of the high susceptibility of the animal pole to 

 noxious influences. 



This author (Child '11, '12, '13, '14) has shown that if a ciliate 

 infusorium or a planarian be subjected to the influence of lethal 

 solutions of certain toxic substances the disintegration resulting 

 in the death of the animal w^ill proceed gradually from the anterior 

 towards the posterior end of the body. The same results were 

 obtained also in other adult invertebrates. In this manner a 

 definite gradient of susceptibility was demonstrated to exist 

 along the chief body axis. 



