Artificially Produced Cyclopean Fish 305 



MORPHOLOGY OF CYCLOCEPHALIA 



It was mentioned above that the optic outpushings became 

 visible on the sides of the brain at about thirty hours after fertihza- 

 tion. At this time the brain of Fundulus is a soHd mass of cells 

 without a central ventricle. The optic bodies are not hollow at 

 first, but are solid outpushings which later develop central cavities. 

 The cavity generally forms in the optic outpushings while the 

 brain is yet solid. Dareste ('91) has advanced hypothetically 

 the idea that if the anterior vesicles of the brain did not develop, 

 a contact would be maintained between the "parties retiniennes" 

 up to a certain time and consequently they would unite to give a 

 median cyclopean eye. If this were in reality the cause of cyclopia 

 we might expect all Teleosts like Fundulus to be normally cyclo- 

 pean since in them the eyes arise while the brain is without a ven- 

 tricle. Spemann ('04) finds in cyclopean Triton embryos that 

 although the tube is hollow, the eye anlagen are defective from 

 the beginning. The matter of a closed brain would then seem 

 to be unimportant in a consideration of the causes of cyclopia. 



a Earliest Indication, Exact Position and Condition of the Eye 



When forty-one hours old, the brain as shown in trans-section 

 by Fig. 28, is still a solid mass. The two normal optic out- 

 pushings have developed small cavities but no indication of 

 invagination of the vesicles or ectodermic lens structures are seen. 



A section through the optic region of an apparently one-eyed 

 monster when forty-one hours old, is shown by Fig. 29. The 

 sections of this series show only one ventro-lateral eye vesicle. 

 The vesicle is large and distinctly optic in nature, while on the 

 opposite side is shown a thick cellular wall from which the brain 

 is becoming separated. Such an individual resembles more a 

 Monstrum mono phthalmi cum asymmetricum than it does the 

 cyclopean type. 



Fig. 30 shows a transverse section through the eye of a forty- 

 nine hour embryo which exhibits a perfectly clear case of cyclopia. 

 Here the brain is beginning to form a cavity and the optic vesicle 

 with a well defined central cavity is just invaginating to form the 



