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other parts of the brain. It would be interesting to know if such an 
embryo were sensitive to light through its retina, but I have not yet 
found a satisfactory test. 
The Pigment Layer of the Retina. 
There is some evidence such as is afforded by Embryo 121 (see 
Figs. 1 and 2) to show that the pigment layer of the retina may be 
developed from undifferentiated brain tissue under the influence of the 
inner retinal layer; but I shall defer the consideration of this point 
until my full paper is ready. 
The Nasal Cavities. 
Embryo 417b, 3,5 mm long. The pigmented nasal plate of the 
right side was removed before the invagination had begun. The embryo 
was killed the seventh day after the operation. Both nasal organs 
were in connection with the pharynx and fibres from both had also 
grown into the brain. 
Embryo 326, 3 mm long. The left anterior half of the brain 
anterior to the optic vesicle was removed without removing any ecto- 
derm. In this embryo no pigmentation or other external evidence of 
the nasal plate was visible at the time of the operation. The left 
nasal plate and fossa developed simultaneously with that of the right 
side, no difference being noticeable. The embryo was killed the tenth 
day after the operation. The left telencephalic lobe is very short and 
small. The left nasal organ connects with the pharynx, but is situated 
further ventrally and medially than normal lying rather under the brain 
and at a considerable distance from it. It is throughout much larger 
in section than the right normal organ. In its central portion are a 
great many fibres taking up a large part of its parenchyma. They 
run through it in an oblique or longitudinal direction but none seem 
to leave it. There is no connection with the brain. 
Embryo 336, 3,5 mm. The anlage of the nasal organ at this 
stage is a pigmented thickening of the epithelium, no invagination is 
yet present. A small area of ectoderm above the right optic vesicle 
was removed and the nasal plate with some adjacent ectoderm of the 
same side was transplanted on the denuded area. The transplanted 
nasal plate invaginated and seemed to develop as that of the normal 
side except that it was smaller. The embryo was killed the fourth 
day after the operation. The transplanted nasal anlage had developed 
a thick cord of cells extending caudally from the nasal pit similar but 
smaller than the normal anlage. The entire anlage lay above the eye 
