ORIGIN OF MONSTERS 547 



makes the impression of an ill-differentiated cornea. Between 

 the lens and the yolk there is to be seen a very wide space filled 

 with a plasma-Uke mass and lymphocytes. In farther sections 

 an optic cup and still further a small unilobed, oedematous brain 

 comes into view (fig. 58). A part of the pigment epithelium is 

 also seen in this section; it partly surrounds a nerve trunk 

 (apparently the optic nerve?), whose course is a very tortuous 

 one. In further sections posterior to the lens the rods-and-cones- 

 layer of the retina can be easily recognized (fig. 59),. while the 

 other layers seem to be ill-differentiated and (owing to blastoly- 

 sis) considerably intermingled. 



In still further sections through the meroplast the lens and the 

 optic cup of the second eye component gradually come into 

 view (fig. 60). The optic cups of both eye components are 

 fused for the most part and if the whole series of sections be 

 followed out, only the bottoms of the optic cups appear to be 

 separate. The analogy between the morphology of this case 

 of solitary synophthalmia and that of bilentic synophthalmia 

 described in a preceding chapter of this paper (cf. p. 503) is 

 evident. 



What is the morphogenesis of this meroplast? The fusion 

 of two early undifferentiated eye anlagen has evidently occurred 

 after chemical blastolysis has eliminated a wedge of intermediate 

 tissue. This blastolytic process has probably taken place while 

 the egg was in the toxic solution, while on subsequent transfer 

 to pure sea-water owing to increased imbibition of sea-water, 

 resulting from the treatment of the eggs with acids, osmotic 

 pressure has apparently destroyed all of the embryonic primor- 

 dium excepting the small part which has given rise to the synoph- 

 thalmic head fragment. 



One more egg with a solitary eye may yet be briefly described. 

 In figure 38 which illustrates it, there can be seen a rather large, 

 tissue fragment with a very large eye. Close to it is a large 

 oedematous (pericardial?) vesicle. Some small blood vessels 

 have also developed, but there is neither a heart nor a continu- 

 ous system of circulation. Owing to the considerable size of 

 the tissue fragment from which the eye arises, as well as to its 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 21, NO. 4 



