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 kpponica, 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 kteral spots on the prothoraxare present (Fig. i). 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. In a 

 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 is found 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 i 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. 



