POSITION OF OPTIC ANLAGE IN AMBLYSTOMA 271 



definitely predetermined in the medullary plate and Spemann 

 believes that cyclopia is due to failure of median medullary cells 

 other than future eye cells then cyclopean eyes ought always to 

 be large or double in size. 



The fact is that these predetermined eye cells in the medul- 

 lary plate in most cases of cyclopia are incapable of perfect dif- 

 ferentiation on account of insufficient energy, so they remain 

 in the brain, or only part of them is capable of difTerentiation 

 and thus small defective cyclopean eyes result. 



The actual 'Lahmungs' or suppression is of the eye material 

 itself. Cyclopia is an eye defect, and an injury of the eye forming 

 material is the cause. The brain may also be defective as an 

 accompaning abnormality, although in some cases the brain, 

 with the exception of the optic tracts and parts, may be struc- 

 turally and functionally perfect, as is indicated by the normal 

 life and behavior of many of the cyclopean Fundulus embryos 

 as well as by the existence of the huge cyclopean ray, Mylio- 

 bates noctula, reported by Paolucci in 1874. 



The chemical substances employed by the author in produc- 

 ing the cyclopean defect and a number of others with which 

 McClendon has obtained similar results, all tend to suppress or 

 arrest the development of the eye material in the brain. This 

 future eye material is assumed to occupy a median position. 

 When the arrest is complete, and necessarily taking place at 

 early stages, no eye parts arise from the brain nor are any dif- 

 ferentiated within the brain substance itself. Thus a completely 

 eyeless individual is produced. 



Spemann states that the eye is capable of differentiation even 

 though it be contained within the brain substance as he has 

 found in amphibia and as MencI recorded in a teleost. It must 

 be realized that these are exceptional cases. A certain amount 

 of energy is necessary for differentiation of the eye to take place 

 even within the brain and when only this amount of energy is 

 present the eye may differentiate within the brain, but when 

 the required energy for any reason is not available the eyes are 

 incapable of any differentiation. Many eyeless individuals have 

 been observed in my experiments which have no indication what- 



