ORIGIN OF MONSTERS 539 



or anteromedian portion of the early, undifferentiated head 

 primordium. In most embryos which exhibit no other than 

 eye deformities, this destructive blastolysis affects the forebrain 

 only, while occasionally the mid-brain, or a part of it, may to 

 some extent be found to be invoh'ed in the process of destruc- 

 tion. Among many embryos which, while being teratophthal- 

 mic, appeared to be 'normal' in other respects, I have found one 

 in which blastolytic fragmentation in the region of the mid-brain 

 (one optic lobe) is very apparent. A transverse section at the 

 level of the mid-brain of the embryo (fig. 13), whose one eye 

 only was defective, the othei' being normal, is shown in figure 

 74. Examination of this figure shows that the left optic lobe 

 (on the right side of the figure) is fragmented, the greater part 

 of it being delaminated in such a manner that a wide furrow 

 resulted between the two fragments of the lobe. The break 

 through the optic lobe is, however, not complete, for if more 

 posterior sections be examined, it can be seen that, at the basal 

 (ventral) part, the lobe is unbroken. This finding, I think, is 

 highly indicative of the blastolytic nature of the process which 

 brings about the defects of the brain. 



Our observations on the brains of teratophthalmic Fundulus 

 embryos agree well with those made on the brains of human 

 ophthalmic monsters. Here, too, the mid-brain and hind-brain 

 usually (in cases where cyclopia is the only deformity present — 

 Ernst '09) are normal while the forebrain is small and unilobed. 

 The single condition of the latter is so well known as to have 

 even led some authors to the assumption that it is responsible 

 for cyclopia. In our opinion it is syngenetic with the deform- 

 ities of the eyes, the olfactory organ and the mouth, i.e., all 

 these deformities are genetically due to the same defect— the 

 blastolytic destruction of a certain (more or less wedge-shaped) 

 part at the anterior end of the early head anlage. 



The chemical alteration which underlies the blastolytic lesion 

 is, as has been pointed out repeatedly in the preceding, the 

 greatest most anteriorly and diminishes posteriorwards along a 

 line corresponding with the future embryo's chief body axis. 

 Most anteriorlv this alteration leads to destruction and elimina- 



