548 E. I. WERBER 



peculiar shape, the interpretation of the case in toto appeared 

 difficult. 



In sagittal sections, however, it was recognized that the large 

 size of the meroplast was due to oedema. In figure 81 is pre- 

 sented such a section which is near the longitudinal ixiidline of 

 the meroplast. The view is that of a transverse section of a 

 rather distorted diencephalon and a large, longitudinally sec- 

 tioned eye. The latter is well developed; the pigment layer is 

 rather delicate, the rods-and-cones-layer of the retina, which 

 is considerably distorted, is well differentiated, as is also the 

 lens. Between the pigment epithelium and the other retinal 

 layers of a large part of the eye there is to be seen an oedematous 

 space filled with plasma and lymphocytes. This oedematous 

 condition is responsible for the unusually large size of the eye, 

 as well as for the distortion of the retina. For, in further sec- 

 tions, where the oedematous space gradually disappears, the 

 wall of the optic cup has a practically normal appearance. Both 

 the eye and the brain are situated between the yolk-sac and the 

 yolk. The brain, while very close to the eye, is partitioned off 

 from the latter by an ectodermal lamella. It thus appears 

 to be almost enclosed in a separate cavity which is surrounded 

 by the blastoderm on all sides but one. This cavity is, however, 

 not entirely taken up by the brain, for as seen in figure .81, it 

 contains several large empty spaces filled with either plasma or 

 leucocytes. These findings explain the large size of the mero- 

 plast as well as the peculiar shape of the tissue fragment from 

 which the eye has arisen. 



The three cases of solitary eye described above furnish ample 

 evidence for the fact that a fragment of the medullary plate 

 may be capable of independent development to such a high 

 degree as to give rise to a well differentiated eye. 



A somewhat similar case has been recently reported by J. Loeb 

 ('15, p. 96). In the monstrosity which he produced from a 

 Fundulus egg by low temperature ''one eye with a lens and the 

 tail was all that could be recognized" (cf. Loeb's fig. 13). His 

 interpretation is to the effect that ''the whole embryo had devel- 

 oped but the eye had survived while the other parts perished." 



