ORIGIN OF MONSTERS 513 



One more case of perfect cyclopia may now be described. 

 On examination of the embryo in toto (fig. 7, p. 488) it was seen 

 that the cyclopean eye is lacking the lens. This may be attrib- 

 uted to the circumstance that the optic vesicle came into con- 

 tact with damaged head ectoderm. 



On examination of sections (fig. 48) conditions are found which 

 again point to blastolysis (dissociation and dispersion) and subse- 

 quent regulation as the factors responsible for the formation of 

 perfect cyclopia. The retina is defective, its rods-and-cones 

 layer being fairly well developed on one side and less so on the 

 other side of the optic cup. The ganghonic granular and fibrous 

 layers appear to be scattered and intermingled. Se^'eral insular 

 accumulations of retinal cells surrounding fibers can be observed 

 resembling the 'retinal rosettes' recently described by Nehl ('14). 

 The oedema evidenced by numerous large tissue spaces in the 

 eye and in the brain (which latter is highly defective and un- 

 paired), and the distension of the cranial cavity are very likely 

 due secondarily to blastolytic action, the blood vessels, owing to 

 destruction of embryonic material, having failed to develop into 

 a continuous system of drainage. Nothing can be seen in any 

 of the sections that would indicate a fusion of two optic anlagen. 

 Only one optic nerve is seen to pass out of the eye and enter the 

 brain. The complete absence of the olfactory pits and the 

 mouth (the latter coming into view in sections behind the eye) 

 also strengthens the evidence for blastolytic action (dissociation 

 and dispersion) of the environmental modification employed in 

 the experiment. Owing to this action, evidently, the ophthalmo- 

 blastic material of one side has been destroyed, while that of 

 the other side has, through subsequent reparation, come to 

 occupy a median position. 



e. Monoyhthalmia asyvimetrica. I shall now attempt to show 

 that the same morphogenetic factor (blastolysis) is responsible 

 also for the genesis of other cases of teratophthalmia. They are 

 exemphfied by embryos in which both eyes are present in the 

 typical later position in the head, one of them being normal, 

 while the other is small in size and rudimentary in structure, 

 by embryos in which one of the eyes is dislocated (ophthahnic 

 ectopia), and by asymmetrically monophthalmic embryos. 



