ORIGIN OF 'independent' LENSES 357 



indicates that the ophthalmoblastic material of each side has been 

 fragmented by blastolytic action of the modified environment 

 into two parts, one of which was capable of differentiating almost 

 as much as in normal development, while the other attained only 

 a rather low degree of differentiation. 



The longitudinal axes of both eye bulbs are dorso-ventral in- 

 stead of transverse as they should be in the fish. This deviation 

 in their position in relation to the brain is, undoubtedly, also 

 due to blastolytic dissociation and subsequent readjustment of 

 parts. Owing to this dissociation the optic anlagen have during 

 their progress towards the unusual position which they finally 

 have come to occupy, left fragments of optic material in their 

 trail, and have in this way stimulated a number of lentoids to 

 arise, which can be found in a number of sections, most promi- 

 nently, on the right side, between the last part of the eye and 

 the rudimentary optic cup of the same side (fig. 6) At this 

 point (the region of fragmentation of one original eye anlage 

 into two) a loose mass of apparently disintegrated tissue, only 

 the nuclei of which have for the most part remained, can in a 

 number of sections be observed to extend all the way from the 

 rudimentary optic cup with which it is continuous into the 

 oral cavity. The latter is at this point defective, a part of its 

 cartilaginous roof lacking. Careful examination of sections shows 

 that the nuclei of the disintegrated tissue mass are mainly of two 

 sizes. The impression is gained that these nuclei are the rem- 

 nants of potential retinal cells, the large ones possibly correspond- 

 ing to the cells of the ganglionic layer while the small ones to 

 those of one of the molecular layers. If we imagine that the 

 disintegrated tissue mass was fragmented and dispersed from 

 the earliest primordium of the eye of this side, it is conceivable 

 that many of its cells were yet capable of farther development 

 and have made some steps in differentiation. To the latter may 

 be due the differences between the nuclei of this 'syncytium,' 

 corresponding to differences between the various layers of the 

 retina. At any rate, the tissue mass in question suggests for- 

 cibly that we are here dealing with a retinal fragment, which was 

 largely disintegrated after some dififerentiation. It is only neces- 



