ORIGIN OF MONSTERS 519 



The brain is bilobed, but asymetric in regard to its relation 

 to the chief body axis, the hemisphere of the side possessing the 

 eye preceding in sections that of the side lacking the eye. 



The lesion sustained by the early embryo was evidently re- 

 stricted to the left side of its anteriormost part, where it has 

 ehminated the entire ophthalmoblastic material, minute remnants 

 of which have apparently stimulated the differentiation of free 

 lenses. Owing to subsequent processes of regulation, the in- 

 jured side of the head suffered a posteriorward displacement. 

 This would account for the small size and unusual position of 

 the left olfactory pit as well as for the asymmetry in the posi- 

 tion of the left hemisphere of the brain. 



f. Microphthalmia and Anophthalmia. Microscopic examina- 

 tion of sections of embryos with very small, rudimentary eyes, 

 or such in which no eyes can be detected in to to have Ukewise 

 disclosed conditions which point to the action of the same 

 dynamic factor that was found to underly the formation of all 

 other eye terata described above. 



The following two examples may suffice: 



On cross sections (fig. 80) of the microphthalmic embryo illus- 

 trated in figure 20 (p. 494) the following view is presented. One 

 eye, while being very small, is seen to be fairly well developed, 

 the retinal layers of the optic cup and the lens being well differ- 

 entiated. The optic nerve of this eye is very clearly seen to 

 enter the optic lobe of the opposite side. The other eye is much 

 more defective. It consists of a rather poorly differentiated 

 optic cup enclosing a lens. One side of the wall of this optic 

 cup is invaginated and partly surrounds another lens. Median- 

 wards from and near to this eye is an undifferentiated mass of 

 apparently ophthalmic tissue with a large well differentiated lens. 



The embryo then, as we see, possesses virtually three eyes, 

 one of which in structure approaches the norm. Of the other 

 two eyes the first is poorly differentiated and possessed of two 

 lenses, while the second is represented by an undifferentiated 

 optic vesicle with a lens. 



The ophthalmoblastic material of both sides has suffered 

 lesions, which resulted in the breaking up of one optic anlage 



