Experiments with Snails, Moths, and Beetles 151 
Other crosses were made between a brood showing no markings 
and yellow cocoons, and striped with white cocoons, and gave 
the usual Mendelian results of splitting and recombination. 
Experiments with Beetles 
In the Californian beetle, Lina lapponica, two types exist, a 
spotted type shown in Fig. 4 and a black type shown in Fig. 6. 
The heredity of these two types has been studied by Miss Mc- 
Cracken. When the beetle emerges from its pupal case the wings 
are nearly pure white. The large median black spot and the 
two lateral spots on the prothorax are present (Fig. 1). In the 
course of ten minutes faint indications of spots appear on the 
wings (Fig. 2), and after fifteen to twenty minutes these become 
more distinct, as seen in Fig. 3. In the course of forty-five min- 
utes the spotted type has reached its final condition (Fig. 4). 
The black type passes through a stage like that of Fig. 3 to that 
of Fig. 5, and finally after forty-five minutes to Fig. 6. Ina 
sense the black type passes through the spotted type, the back- 
ground becoming as dark as the spots themselves, so that the 
spots can no longer be seen. 
If these two’kinds of individuals are collected at random and 
isolated in pairs, it isfound that the spotted pairs sometimes (in 
half the cases) produce their own kind only, and in other cases pro- 
duce both spotted and black types. There are no intermediates. 
When the blacks are paired they produce in some cases broods 
that are all black, and in other cases broods in which some of 
the individuals are black and some are spotted, in the proportion 
of 1 spotted to 1.7 black. 
If a black and a spotted individual are paired, mixed broods 
are produced with a preponderance of the spotted type. 
The results for the second generation are especially interesting. 
If those broods from black parents are picked out in which all 
of the individuals are black and these are paired, all of their off- 
spring, without a single exception (in 4985 cases), are black. 
The third generation is also black. Hence there is a pure race 
of blacks. The black is evidently the recessive form. 
