ORIGIN OF MONSTERS 517 



has, then, on this side affected both the potential olfactory and 

 eye anlagen, fragmenting the one and delaminating and dislo- 

 cating the other. The effect is an increased number of olfac- 

 tory pits and ophthalmic heterotopia. 



The same morphogenetic factor was apparently responsible 

 also for the conditions found in the embryo in figure 16, p. 492. 

 Its head is unusually large and suggests oedema. The left eye is 

 lacking entirely and a free lens is found in its place. The right 

 eye is defective, the optic cup being C-shaped and the large 

 lens greatly protruding, owing to the absence of an anterior 

 chamber. 



In the most anterior sections only the 'independent' lens is 

 seen which is not yet fully differentiated. In the next sections 

 there comes into view the lens of the right eye and two olfac- 

 tory pits. The latter are observed to be so closely approximated 

 as to be partly contingent on their median borders, and to form 

 an angle of about 90 degrees. More posterior sections show 

 that the optic cup of the eye is only anteriorly C-shaped, while 

 it is complete, though small, in its posterior part. The part 

 of the section where the (lacking) left eye should be, is occupied 

 by very loose mesenchyme the interstices of which are filled 

 with plasma. The retina is very well differentiated and one 

 optic nerve can be traced to its entrance into the brain hemi- 

 sphere of the opposite side. A very remarkable feature is pre- 

 sented by the sections through the base of the eye (fig. 76). 

 Here, ventral to the brain and lateral from the eye from which 

 it is entirely separated, there can be observed a very small optic 

 cup-fragment with all layers (pigment and retinal-rods and 

 cones) perfectly differentiated. This is evidently a dislocated 

 but fully differentiated remnant of the destroyed ophthalmo- 

 blastic material of the left side. 



Essentially similar conditions were found in the embryo illus- 

 trated by figure 15 (p. 490). A ventral view of it is presented in 

 which it can be seen that the right eye is lacking and its place 

 is occupied by the mouth. The left fin is about half the normal 

 size, and no other abnormahties were found on examination of 

 the embryo in toto. 



