PARTULA RADIOLATA. 59 
type. The fulva adults contained 6 yellowish, 1 whitish, and 3 brown young (fig. 
59, plate 11). As the flavea adults number 36 in the whole colony to 19 pallida, 
while the yellowish young amount to 36 as compared with 37 whitish individuals, 
evidently some of the embryonic flavea snails are so pale as to be indistinguishable 
from pallida; this conclusion is certainly preferable to the supposition that the 
association is rapidly changing from one in which flavea is dominant to one 
characterized by a preponderance of pallida. A second important point is that the 
majority of the young produced by fulva adults revert to the lighter phases, while 
the others repeat the parental character of color unmistakably. Obviously the 
three color-classes of this association interbreed. 
The discussion becomes more involved when it shifts to the associations which 
comprise the darker classes of strigata, strigata-helix, and bicestata, as in the local 
series from the Apra Region (table 24). Embryonic shells of the three types are 
shown in figures 60 to 64, plate 11. The strigata form is light brownish with a 
similar apex (figs. 60, 61, plate 11), and it is quite different from the fulva type of 
young. In the strigata-helix young there is a definite revolving band on a brownish 
ground-color (fig. 62, plate 11). The banded pattern of the bicestata young is 
evident in the actual specimens (figs. 63, 64, plate 11) by virtue of the contrast 
between the light ground-color and the bands. While errors in determination are 
by no means entirely excluded, yet the distinctive characters are so clearly dis- 
played by the majority of the young as to render the statistics really significant. 
In the eastern Cabras association (table 24), the flavea type reproduces its own 
kind without exception; this is at least suggestive that the lighter and more uniform 
coloration is a Mendelian dominant with reference to darker color characters. The 
strigata adults produce all three kinds of offspring, but with a high preponderance 
of their own kind, and the same is true of the bicestata adults. The striking 
features of the western Cabras association are the exclusiveness in heredity of the 
bicestata pattern, the transmission of the strigata coloration with nearly equal 
strictness, and the production of both strigata and bicestata young by the strigata- 
helix parents. In the case of the Orote material, which includes some light but recog- 
nizable fulva, an additional point of interest is the lighter color of the young from 
such adults; undoubtedly some were destined to become darker with age. 
From the facts recorded above, even when due allowance is made for unavoid- 
able errors of observation, it is clear that the animals of the distinguishable color- 
classes are genetically inter-related and have not become so isolated in the physio- 
logical sense as to be incapable of mutual interbreeding. 
