366 Bee. Al GnING 
Sudden and unexpected changes in a character of a pure race have been 
known by naturalists, as well as by practical breeders, to occur from time 
to time in both animals and plants, and are called in popular language 
‘ sports.” Sometimes, no doubt, these sports are due to the reappearance 
of a latent or hidden character, which existed in the ancestry of the 
organism ; at other times the so-called sports may be due to a sudden 
change in the constitution of the individual or of the germ cell from which 
it sprang, so that the character may be said to originate in the particular 
individual, instead of being inherited from its ancestors. To new char- 
acters which originate suddenly in this way the name mutation has been 
given. The red eye of Gammarus may be described as a mutation, appear- 
ing in the third generation of a wild animal which had been subjected to 
the artificial conditions of captivity. 
The red-eye is transmitted from parent to offspring, and it behaves 
quite in a typical Mendelian way, red eye-colour being recessive (like the 
green pea), and black eye-colour dominant (like the yellow pea). For use 
in the hybridisation experiments a pure black stock, obtained from 
Chelson, was kept and thoroughly tested. The stock was maintained 
for over three years, the offspring and descendants being all examined at 
different seasons of the year, and in no single case has one with red eyes 
been found amongst them. Numbers of pairs of red-eyed animals, also, 
have been bred together, each pair being kept in a separate vessel. The 
young have all been examined for eye-colour, and the experiment has 
been continued to the fifth generation and beyond, well over a thousand 
young having been recorded. A black-eyed animal was never once found 
amongst them. Both the wild, black-eyed Gammarus, therefore, and the 
red-eyed variety, which arose in the Laboratory, breed perfectly true to type. 
Red-eyed animals were mated with pure black, the cross being made 
in both ways, red female with black male, black female with red male. 
In the early experiments 3,779 young ones were examined and recorded. 
Without exception the eyes were black. Clearly, therefore, black is 
dominant and red recessive. 
The black-eyed hybrids obtained from the cross between black and red 
were mated together. They produced altogether 4,393 young, of which 
3,327 were black-eyed and 1,066 were red-eyed. (See Diagram 6.1.) This 
is a very close approximation to the 3:1 ratio. There are 32 reds too 
few on a total of 1,066 reds. This may be due merely to chance, or it 
may be due to the fact ascertained during the course of the experiments 
that the red-eyed animals are not quite as vigorous and healthy as the 
black-eyed. The deficiency in the number of reds may therefore mean 
that more red than black failed to survive whilst the eggs were 
developing in the brood-pouch of the mother. 
