A CASE OF CYCLOPIA 235 



of the third. ventricle (figs. 11 and 23). This obhteration of a 

 part of the ventricular cavity is not necessarily the result of 

 the growth conditions producing cyclopia; but probably these 

 growth conditions rendered such an obliteration more liable to 

 occur in this region than elsewhere. 



Mechanical considerations 



Stockard has shown that the condition of cyclopia may be 

 produced at will in fish embryos in a high percentage of cases by 

 treating the eggs with MgCl2 or Mg(N0,-!)2 solutions (24 and 26). 

 He was thus able to study histologically a great number of cases 

 in fish embryos otherwise perfectly normal. His observations 

 showed that "the cyclopian defect is present from the first in 

 the same condition that it will continue throughout develop- 

 ment" (25). This statement was subsequently (27) somewhat 

 modified by further experimental work, for it was found that 

 cyclopia could be produced in a small percentage of cases by 

 the action of magnesium chloride, even after segmentation had 

 gone as far as the periblast stage (15 hours). Eggs older than 

 the fifteen-hour stage were not affected by the Mg solutions. 

 Thus, although cyclopia is not necessarily of germinal origin, 

 the growth inhibition begins at so early a stage of embryonic 

 life that it practically amounts to absence of certain areas dur- 

 ing development. In other words, cyclopia is not the result of 

 fusion of parts originally separate, but is due to absence during 

 development of certain parts normally separating the eye anlagen. 



Cyclopian monsters belong to that class of bilaterally symmet- 

 rical beings which have been termed by Wilder (28) 'cosmobia.' 

 Development in these cases proceeds in a orderly fashion until 

 some mechanical difficulty arises which cannot be overcome by 

 the individual and death results. In fish the development in 

 cyclopian forms 'goes on until the yolk supply is entirely used up, 

 when the animal dies of starvation unless suitable food is artifi- 

 cially provided. In this connection it is also of interest to note 

 that the absence of tissue anlagen does not postulate a non- 

 functional ruervous system, for individuals which have been kept 

 alive and observed, reacted to stimuli in a quite normal fashion. 



