ORIGIN OF MONSTERS 531 



A small part of the egg in the earliest stages of development 

 corresponding to a restricted area at the anterior end of the 

 future embryo's body sustains a chemical lesion, i.e., it becomes 

 so altered chemically as to be incapable of the reactions necessary 

 for its further normal development. The part of the egg thus 

 incapacitated, is potentially the region anterior to and between 

 the future optic anlagen or even the region of those anlagen. 

 This affected area goes on developing up to a certain point 

 beyond which, owing to the exhaustion of its chemical capacities, 

 it loses its correlation with the whole, i.e., with the rest of the 

 embryo-forming material and becomes eliminated by dissocia- 

 tion. Or, the affected area may, at that critical point of chemi- 

 cal incapacity, be permanently arrested and retain the charac-- 

 teristics of this early stage of development (some cases of 

 anophthalmia), while the rest of the embryo may develop and 

 differentiate further. 



The size of this restricted area of blastolytic lesion at the 

 anterior end of the potential embryo's body axis is probably 

 subject to considerable variation. Thus it may comprise the 

 mass of cells which would normally correspond to the future 

 interocular area and cause an approximation of the potential 

 optic anlagen or, it may extend over the latter ones and elimi- 

 nate parts of them, while the uninjured parts would fuse after 

 an approximation resulting from the healing of the wound, and 

 form any one of the various degrees of the synophthalmic con- 

 dition. Again, the injured region may comprise parts of the 

 ophthalmoblastic material of both sides and very little of the 

 potential interocular area. The remnants of the optic anlagen 

 may develop and differentiate fully into eyes of strikingly small 

 size of the microphthalmic monsters. Or, the lesion may com- 

 prise the whole of one optic anlage and little or no material of 

 the future interocular area. In that case the embryo will develop 

 into a perfectly cyclopean embryo, if, owing to subsequent regu- 

 lation, the uninjured potential optic anlage is shifted median- 

 wards, or into an asymmetrically monophthalmic monster, if 

 no such change in the position of the uninjured or less injured 

 ophthalmoblastic material takes place. AVherever in such cases 



THE JOCRNAli OF EXPERIMENTAL ZOOLOGY, VOL. 21, NO. 4 



