ORIGIN OF MONSTERS 507 



malformation. These differences are apparently such of degree 

 only, and probably due to differences in the degree of intensity 

 of action of the same morphogenetic factors. 



Synophthalmic cyclopia is characterized by the presence in 

 the embryo of a single median eye usually of a larger size than 

 the normal eye, not composite in its appearance in toto but very 

 markedly so on microscopic examination of sections. The fol- 

 lowing two cases may illustrate this deformity. 



In figure 5 (p. 488) is presented an embryo which has a single, 

 very large, well-formed, median eye, which on examination in 

 toto reveals nothing that would suggest its composite character. 



On microscopic examination of transverse sections the most 

 anterior sections still present the appearance of a solid non- 

 composite eye, w^hile at about the level at which the lens begins 

 to appear in the sections, the eye-cup discloses its composite 

 character the more the further the sections are followed out 

 posteriorw^ards, until at the level of the optic lobes this condition 

 of fusion is seen to be very striking. In this region, as well as 

 somewhat anterior and posterior to it, the optic cup presents 

 the appearance of the horizontal section of a funnel (fig. 65). 

 The small end of this funnel is blind and enclosed by the brain, 

 into the substance of which it is seen to dip to a remarkable 

 depth. This funnel-shaped eye is unusually large and the brain 

 is strikingly small. The structures of the optic cup are well 

 differentiated as far as the large part of the 'funnel' is concerned, 

 for here the pigment layer and all layers of the retina are present 

 in their typical appearance. In the small end, however, there 

 are only slight traces of the rods-and-cones layer between the 

 outer margins of the 'funnel' and the brain, while of the other 

 parts of the retuia the fibrous and ganglionic layers are present 

 throughout and are seen to be in continuation with these parts 

 of the large end. 



The interpretation of the morphogenesis of this cyclopean eye 

 is facilitated by examination of sections of the entire head. The 

 following conditions are revealed by it. The olfactory pits are 

 fused. The fore-brain is unusually short and unpaired, while the 

 mid-brain is bilaterally symmetrical but not distinctly divided 



