398 Charles R. Stockard. 
a seventy-six hour embryo; it is scarcely conceivable that an 
optic vesicle arose at about the thirty-fifth or fortieth hour, 
came in contact with the ectoderm and entirely disappeared, 
leaving no trace of itself by the seventy-sixth hour. Further, 
the lens in these cases must continue to develop and differentiate 
independently, which is contrary to the position held by Spemann 
(05), Lewis (07) and LeCron (’07) for the frog and salamander. 
Fig. 2 shows a fish nineteen days old with two well formed 
lenses of normal size lying in contact with two small irregularly 
shaped masses of heavy black pigment. In sections, figs. 23 and 
24, the lenses are found to be perfectly formed and the two dark 
spots are shown to be masses of choroid tissue or retinal pigment 
without a definite retina or other associated eye parts. The lenses 
may owe their existence to the choroid spots but the latter have 
failed to influence the size or manner of development of the former. 
If the origin of these lenses was due to the influence of the choroid 
areas we have a striking example of how very small an amount of 
optic tissue may call forth a lens. Many instances will be given 
to show that extremely small amounts of optic tissue touching 
the ectoderm will stimulate a lens to form, yet these cases will in 
no way weaken the evidence that lenses do at other times form 
entirely independently. 
A fish is illustrated by fig. 38 with two small defective eyes 
deeply buried in the head. The right eye possesses a lens but 
the left faces ventrally into a mass of mesenchyme and is without 
a lens. In front of the left eye is shown a lens in an extremely 
anterior position but completely separated from the eye, and the 
concave surface of the cup is not directed towards this lens. Fig. 
4 proves the case by showing two slightly small eyeseach possess- 
ing its own lens, while somewhat in front and between the two 
eyes lies a perfectly isolated and independent lens. It is evident 
that this supernumerary lens is independently formed and not 
due to a stimulus trom either of the eyes, since each has its 
own. lens. 
