204 M. F. GUYER AND E. A. SMITH 
two (4A4, 4A5) the defect was on the left side as it had been in 
the father, while in the third (4A1) it was the right eye that 
showed the abnormality. In the right eye of 4A1 the iris, al- 
most transparent, was interrupted below (coloboma) and did not 
expand or contract (pl. 1, 4A1). The eye as a whole was smaller 
than the left eye. The lens likewise was smaller and was opaque, . 
causing the peculiar silvery hue already described. ‘These same 
defects appeared in the left eye of 4A4 and of 4A5 (pl. 1, 4A5). 
Another litter (fig. 5), 4B series, from the same parentage was 
born March 14, 1918. One female, 4B1, had a left eye like her 
father with no trace of iris or pupil (pl. 1, 4B1). The eyeball 
was so small and collapsed that the condition of the lens could 
not be determined. The eyes of the remaining five (four males 
and one female) were normal in size and appearance. 
The female, 3A2, was next bred to a male from normal stock, 
and on July 26, 1918, gave birth to six normal-eyed young, the 
4C series. When bred to another normal male, she again, on 
December 24, 1918, produced six young in which the eyes showed 
no abnormalities (4D series). Finally she was again mated to 
her brother 3A1, and on May 5, 1919, brought forth eight young. 
One in this litter, known as 4E1, had both eyes defective, but 
it died before the sex was determined. 
It will be noted that each of the three separate times 3A1 and 
3A2 were bred together some young with abnormal eyes were 
obtained. In all, from this pair, a total of twenty-two offspring 
were secured. Of these, seventeen had eyes which appeared to 
be normal and five had eyes which were defective. This is 
about as near to the 3:1 Mendelian ratio, obtained through the 
breeding of two heterozygotes, as can be approximated in twenty- 
- two individuals. The female parent, however, showed no evi- 
dence of eye defect. When she was bred into normal strains the 
immediate young were always normal-eyed. We have not as yet 
tried to extract the defect from her normal-eyed progeny. It 
may be mentioned in this connection, although the details are 
not discussed till later, that the male of this pair, 3A1, was re- 
peatedly bred into normal strains and always yielded normal- 
eyed young, but we have extracted the defect again from this 
