414 Charles R. Stockard. 
ectoderm and at such a time stimulated the lens to arise. This 
is merely a conjecture and the more recent experiments of King 
(05) and Spemann (’07) on the frog, and the writer’s on the fish, 
would warrant equally well an interpretation of independent 
origin for this lens. 
Returning to observations on monsters we may consider the 
case reported by Menel (’03) which has called forth so many 
explanations and criticisms. This report described the existence 
of an independent lens on each side of the head in an anadidymus 
embryo of Salmo salar which he had possessed since 1899, his 
interest in it being aroused by the contributions on the dependent 
origin of the lens. One of the lenses in this monster was closely 
applied to the brain wall, and in fact lay in a depression in the side 
of the brain; the other lens, however, was completely separated 
from the brain by mesenchyme. Spemann and Lewis have tried 
to explain this case by assuming the existence in the brain wall of 
some optic vesicle tissue or substance which when brought in 
contact with the head ectoderm possessed the power to cause 
the formation of a lens. There was absolutebLy no evidence of 
optic tissue in this brain wall and further, the explanation could 
apply only to one of the lenses, though it scarcely explains the 
origin of either. The second lens, entirely free and with mesen- 
chymatous tissue separating it from the brain wall, was as perfect, 
though not so large, as the other which lay against the brain. 
This lens probably arose and developed freely, just as did so many 
lenses in the fish embryos the writer has studied. 
Menel (’0S) has: more recently obtained other anadidymus 
Salmo embryos and confirms his former observations, finding that 
in such monsters free lenses are present in 25 per cent of the cases. 
Gemmill (’06) has also recorded the frequent occurrence of free 
lenses in the heads of monster trout embryos. 
Schaper (’04) in considering a case of a typical lens develop- 
ment comes to the theoretical conclusion that the lens is by 
nature a primitive sense body similar to the sinnesknospe of 
Amblystoma, and has secondarily taken on its present function. 
It must, therefore, arise independently of the optic vesicle, 
with which it is only recently associated. Such speculation 
