TRANSMISSION OF INDUCED EYE-DEFECTS 201 
TRANSMISSION OF THE DEFECTS THROUGH BREEDING 
Perhaps the most interesting and important result of our ex- 
periments is the establishment of the fact that the defects, once 
secured, may be transmitted to subsequent generations through 
breeding. So far, we have succeeded in passing the condition to 
the sixth generation, and there seems to be no reason why it 
will not go on indefinitely, since the imperfection tends to 
become worse in succeeding generations and also to occur in a 
proportionally greater number of the young. 
At present we have thirty-seven living individuals with 
markedly abnormal eyes. Many more could have been secured 
if all the defective-eyed animals had been mated as frequently 
as possible. Up to the present, however, our chief aim has been 
to pass the defect through as many successive generations as 
possible. 
As an example of increased intensity of the defect in later 
generations, the case of a male (3A1, fig. 5; pls. 1 and 2) with a 
bad left eye may be cited. Many of his grandchildren had both 
eyes abnormal, culminating in two which never opened their 
eyes. Subsequent dissection of the latter showed that minute 
eyeballs were present under the closed lids. This progressive 
intensification of the defect was to be expected, perhaps, up to a 
certain limit, since close inbreeding was practiced. 
A glance at figure 5 shows that sometimes one, sometimes the 
other, and not infrequently both eyes were affected. This irregu- 
lar unilateral and bilateral transmission recalls the somewhat 
similar genetical histories of such deformities as polydactyly and 
brachydactyly. 
Little effort has been made so far to find out just what genetical 
factors are involved in the transmission of the defect. The 
abnormal condition has in general the characteristics of a Men- 
delian recessive. When defective-eyed males or females are bred 
to normal-eyed individuals from other stock, for instance, only 
normal-eyed. progeny result in the ensuing generation. But the 
defect may be made to reappear in subsequent generations if 
appropriate matings are made. A good example of this is found 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 31, NO. 2 
