ORIGIN OF 'independent' LENSES 355 



ing the sections caudalwards, we find in the tenth section (60/x 

 from the tip of the head) the beginning of the lens of the right 

 eye. In the section preceding it is seen the capsule of the lens on 

 two sides of which several small lentoids are noted. The lentoid 

 mass at the base of the brain is no longer seen at this level; 

 only a few very small lentoids can be observed in this position 

 in the eleventh and twelfth sections. In the latter there appears 

 also the first indication of the pigment layer of the left eye. 

 Two sections more caudalwards the optic cup of the right eye 

 begins to come into view. At this level the optic cup of the 

 left eye can already be clearly distinguished. Its pigment layer 

 is of a dark brown hue instead of a solid black, which is due to 

 the fact that the pigment cells are considerably dissociated. 

 The layer of rods and cones, while not fully differentiated, is, 

 however, clearly discernible. All the other layers of the retina 

 are spread out far beyond the limits of the optic cup into a con- 

 tinuous mass which reaches the lens of the other eye and goes all 

 around the unusually small oral cavity. From the epithelium of 

 the latter there arise several small lentoids which are in contact 

 with this blastolyzed retina. Four sections more caudalwards 

 the mouth disappears, its place being taken up entirely by six 

 small lentoids which are partly in connection with each other 

 through lens fibers. In this section (fig. 4) and in three more 

 succeeding sections the dissociated pigment layer of the left eye 

 presents a strange appearance. It bulges out on one side of the 

 optic cup to form a very large pocket into which a part of the 

 retina dips. This pigment 'pocket' corresponds to a part of the 

 apparent duplicature of the pigment layer of the left eye seen in 

 toto in figure 1 . The left eye possesses no lens but its blastolyzed 

 retina surrounds the six oral lentoids spoken of above, which in 

 more posterior sections increase in number and form a rather 

 dense cluster. A number of small lentoids can be observed also 

 in the epidermis ventrally from the eyes. 



The optic cup of the right eye is, as compared with its large 

 lens, strikingly small and its tissues, while dissociated, are much 

 less so than those of the other eye. However, the blastolytic 

 dissociation of this eye is plainly discernible in posterior sections. 



