270 CHARLES R. STOCKARD 



modified types which are at least closely related to the series in 

 manner of origin, though they may not actually intergrade. 

 (We are now considering only the cyclopean series, not the mon- 

 ster monophthalmica asymmetrica which will be dealt with later.) 



One finds on referring to my paper of 1909 (p. 293) that the 

 cyclopean series, A to G, passes from the normal individual 

 through different degrees of association of the two eyes to a 

 median cyclopean eye only as large as one normal lateral eye, 

 then to a cyclopean eye of smaller dimensions until it is extremely 

 minute and may finally be deeply buried beneath the brain as 

 a small pigmented vesicle, as is shown in figure 52, page 321. 

 Only one step further and the eyes fail to arise entirely so that 

 eyeless individuals exist which with a slightly greater power of 

 differentiation or more developmental energy might have given 

 cyclopean monsters. The last assumption is warranted since 

 these eyeless specimens actually resemble the cyclopean monsters 

 in other structures; for instance, the mouth is a narrow pro- 

 boscis similar to that in the cyclopean monster instead of the 

 usual laterally spread mouth of the normal embryo. 



Why should every step and gradation in this series exist if 

 several, or any of the conditions are of a different quality or 

 type? It seems certain that one examining the large number 

 of cyclopean fish on which* my study was based would be forced 

 to admit the correctness of the statement that these individuals 

 exhibit different degrees of one and- the same defect. 



The question then follows, if cyclopia were due, as Lewis, 

 Spemann and others assume, to a failure to develop of median 

 medullary tissue so allowing the eye anlagen to come together 

 in the median plane and fuse, why is not e^^ery cyclopean eye 

 equal in mass to the two normal eyes fused? Spemann does 

 not suggest in any place that eye material also fails to arise. 

 He shows in his recent experiments that the future eye is fully 

 laid down in the medullary plate. Not only is the eye present 

 in the medullary plate but the cells destined to form different 

 layers are distinct. Spemann found that certain cells cut out 

 of the medullary plate and planted in more posterior positions 

 formed only the tapetum nigrum layer. If the eye is thus so 



