516 E. I. WERBER 



thus be considered as a part of the optic lobe, from which it was 

 for the greater part delaminated. The ear of the left side is 

 lacking entirely, and it stands to reason that its absence is due 

 to blastolytic elimination of the otoblastic material of this side. 



Very striking evidence of blastolysis can be observed in the 

 embryo in figure 17 (p. 492). It hatched prematurely on the 

 twenty-eighth day, when it was drawn and killed. The yolk- 

 sac is still very large and the embryo is curved. Only the left 

 eye is in the usual position m the head whjle the right eye is 

 found to be strangely dislocated. It is seen extending between 

 the right mandibular arch and the yolk, in which it is well im- 

 bedded, covered by the yolk-sac. 



Examination of sections reveals the follo\\dng conditions. The 

 left eye is well differentiated, but not quite normal. It lacks 

 the anterior chamber and the \dtreous body, while the iris is 

 rudimentary. An optic nerve is present and can be followed 

 out to enter the hemisphere of the opposite side. The brain is 

 apparently normal everywhere. In the sections at the level of 

 the medulla and semicircular canals there comes into \dew the 

 heterotopic eye (fig. 75). It is enclosed between the yolk and 

 the yolk sac and is in proximity to the heart. Between the 

 heart and the dislocated eye very large l>aiiphocytes are seen. 

 The eye is as well differentiated as the orthotopic left eye and is 

 oval in shape, which may perhaps be due to its extra-orbital 

 development. It lacks a pupil and the vitreous body, while the 

 iris also appears to be defective. No optic nerve could be 

 found. 



An important clue to the genesis of these malformations is 

 furnished by the condition of the olfactory pits. The latter 

 can be followed out very satisfactorily in the most anterior sec- 

 tions. Antero-median from the left (orthotopic) eye there is 

 one olfactoroy pit — in its normal position. On the right side, 

 however, (where the eye has been dislocated) there can be seen 

 in sections somewhat more posterior, as many as four minute 

 olfactory pits. It seems obvious that these four small olfactory 

 pits have developed from four fragments of the dissociated 

 potential anlage of the olfactory pit of this side. Dissociation 



