CYTOPLASMIC INHERITANCE 183 
indefinitely. Such bodies might not only produce 
passive products, like starch or pigment, but even 
active enzymes, which, interacting with other 
products of development, might. determine the 
characteristics of the race. 
Structures like the shell and the yolk of eggs are 
purely maternal in origin, but since they do not have 
the power of growth and division, they are not able 
to perpetuate themselves indefinitely, nevertheless 
they may determine certain characteristics of the 
embryo, and to this extent may appear to influence 
the hereditary characters of the generation to which 
the embryo belongs., For instance, the females of 
certain races of silkworm moths have white eggs, be-. 
cause the shell is white. If such eggs are fertilized by 
sperm of another race, that has eggs with a domi- 
nant green colored shell, the shells are nevertheless 
white. Conversely when the green eggs of a female 
moth of the green egg race are fertilized by the 
sperm of a male of a white egg race, the color re- 
mains green. When the moths develop from either 
of these two kinds of hybrid eggs, one white, one 
green, they lay only green eggs, because in the hybrid 
the factor for green dominates and determines the 
color of the shell that is produced in the new eggs. 
These green eggs give rise to moths, three of which 
lay eggs that are green to one that lays eggs that are 
white, showing that here there is only the ordinary 
case of Mendelian inheritance, which is obscured, 
however, when the characters of the young embryo 
are considered, because, as has been shown, these 
