Warren Harmon Lewis 149 
cups and the lenses are further differentiated. Fig. 42 shows such a 
transplanted eye fully as large, if not larger, than the normal one (Fig. 
43), the optic cup is as far advanced in its differentiation and the lens 
is as large and as far advanced in its differentiation as the normal one. 
The position of these transplanted eyes varies considerably and hence 
the place of origin of the lens. A few of the eyes are anterior to the otic 
vesicle, a number are ventral, some towards the anterior end and others 
towards the caudal end of the otic vesicle. Many of the eyes are caudal 
to the otic vesicle and a few as far caudal as the Wolffian body (see Figs. 
32, 37, 38, 40, and 42). So that the lenses must have arisen from 
numerous different places on the ectoderm. It apparently makes no dif- 
ference where the lens arises in order to have fairly normal development. 
The shape of the early lens varies considerably and seems to indicate 
that it is a very plastic structure conforming often to the peculiar shapes 
of the cup-cavity found in many of the transplanted eyes (see Figs. 7, 9, 
11, 14, and 27). Other factors, probably, also help to modify its shape, 
as pressure of the pupillary margin (see Figs. 34 and 38), or pressure 
of surrounding structures (see Figs. 45,47, and 48). The long processes 
which often connect the early lens-bud or vesicle with the ectoderm seem 
to be caused, as I have already explained at some length (see Am. Jour. 
of Anat., Vol. VI, p. 486), by the same factors which tend to force the 
optic cup away from the ectoderm. If the mesenchyme or otic vesicle or 
other structure forces the eye away from the ectoderm while the lens is 
still attached to both, it can be seen how such processes, as shown in 
Figs. 15, 19, 22, and 48, are formed. The normal eye is very firmly 
adherent to the lens during the early stages of its development even up 
to the time when it is pinched off from the ectoderm, so that the lens- 
bud would tend to cling to the optic cup as the latter is forced away 
from the ectoderm by the ingrowth of mesenchyme and an elongation 
of the lens process would result owing to its attachment in the ectoderm. 
I believe that all of the lenses associated with these transplanted eyes 
were formd from the overlying ectoderm through contact stimulus of the 
optic vesicle. The fact that in the later stages the optic cup and its lens 
are separated from the ectoderm by mesenchyme is no proof whatever that 
it was not at one time in contact with the ectoderm and for a sufficient 
length of time to stimulate lens-formation. The part which the mesen- 
chyme plays in the separation of the eye from the ectoderm is probably 
a very active one, and even the normal eye after the lens has separated 
from the ectoderm becomes separated by a layer of mesenchyme from the 
skin. The mesenchyme may, perhaps, be looked upon as an active in- 
