Warren Harmon Lewis é 487 
(DL,,, Fig. 71) which was also killed 4 days after the operation. As 
is seen in Fig. 71, the small regenerating eye and small lens are separated 
from the ectoderm by a considerable layer of mesenchyme. Here there 
was probably a larger area of contact between the regenerating eye and 
ectoderm than in embryos DF,, or DF,,, and so a larger lens-plate and 
lens-bud; there was also probably greater adhesion between optic vesicle 
and lens-bud, so that when the mesenchyme expanded the side of the 
head the lens remained with the eye. In Fig. 72 a similar condition 
is shown, where the area of contact between the small regenerating eye 
and ectoderm is very small and only a few cells enter into the lens-bud ; 
the mesenchyme as it grows in between the eye and ectoderm tends. more 
to separate the lens-bud from the eye than from the ectoderm, and such 
conditions as seem in Figs. 27, 30, 34, 57, and 58 occur. Some varia- 
tions occur, of course, and the lens-bud may form a small vesicle or 
solid body which is separated from both ectoderm and eye, as in Fig. 40. 
King has pictured a somewhat similar condition in rana palustris, 
where the lens-bud is separated by mesenchyme from the optic-cup “ 
(Figs. 5 and 6). She, however, explains this condition by asserting 
that the “lens can be formed from the ectoderm when the optic-cup is 
some distance beneath the surface of the body,” and that “contact be- 
tween the optic-cup and ectoderm is not necessarily the stimulus that 
tends to the development of the lens.” King’s idea that the regenerating 
eye (Fig. 6) was never in contact with the ectoderm (p. 95) is based on 
a misconception of the conditions at the time of an immediately after 
the operation. There is, of course, at this early stage very little mesen- 
chyme in the eye region (see Fig. 3), and the ectoderm lies rather close 
to the side of the brain and the developing eye, and I believe that in the 
early stages of the regenerating eyes in King’s experiments they must 
often have come into contact with the ectoderm and in some embryos 
have stimulated lens-formation. The growth of the mesenchyme here, 
as in my experiments, would tend either to separate the lens-bud and 
optic-cup or to elongate the lens-buds, as in King’s (Figs. 5 and 6). 
It would seem better to explain King’s lens-like structures to have 
been formed in some such manner rather than to assume that the optic 
vesicle can act at a distance, especially when we consider the fact that 
these regenerated eyes of various sizes may remain at varying depths 
beneath the normal lens-forming ectoderm for from 3 to 18 days without 
any signs of lens-formation appearing, and so indicate quite clearly 
1 Roux’s Archiv, Bd. 19, Taf. VI. 
37 
