308 Charles R. Stockard 



is given in Fig. 33. Such a section is most instructive. The 

 condition of the eye is much the same as that shown by the trans- 

 verse section, Fig. 31. The cup is double and two ventral lenses 

 are present. The section passes below (ventral) the diencephalon 

 so that no part of it shows; the telencephalon is indicated in front 

 of the eyes and a thickening of the forward ectoderm shows the 

 nasal plate, posteriorly or behind the eyes the mid-brain is cut 

 in horizontal section. 



A sagittal section of a typical cyclopean embryo is shown by 

 Fig. 34. Here we see the eye and the brain in the third dimension. 

 The telencephalon in front, the diencephalon above the eye, and 

 behind this the large mid-brain with a spacious median cavity. 

 In front of the eye is also shown a median ectodermal thicken- 

 ing, the double nasal pit. The eye is single and exactly ventro- 

 median in its position and connects in a more lateral section with 

 the brain at about the point where the telencephalon and dien- 

 cephalon join. The lens and retina are differentiating into their 

 typical structures. One may obtain a clear mental reconstruc- 

 tion of the Cyclops monster at this age by comparing Figs. 31, 

 32, 33 and 34, the transverse, horizontal and sagittal mid-planes 

 of the cyclopean eye. 



The early stages just described illustrate the cyclopean defect 

 in its various degrees, and the eye throughout its development 

 retains the original condition of singleness or doubleness. No 

 evidence whatever can be found of subsequent fusions during 

 development. Two clearly approximated eyes arise in that con- 

 dition and remain so without fusing to give a double cyclopean 

 eye, and a double eye never attains to the single condition by 

 a more intimate union of its parts. The statement made in 

 my (1907a) former paper, p. 257, that "the fusion of the two 

 components may take place at different periods within a certain 

 limit" is incorrect, as I (1908) have pointed out in a short note 

 on the subject. This statement was one of interpretation and 

 was based on a comparison of late embryos which showed different 

 degrees of cyclopia. It seemed from such an incomplete study 

 that the eyes were more or less double or compound, depending 

 upon the stage in development at which they had become approxi- 



