An Instance of Mutation. 139 



phenomenon : (1) that Coro/s viridis produces different 

 forms under the stimulus of different conditions; (2) that 

 Coccus viridis itself is a mutant from another unstable 

 species. One or both these may be true. If Coccus 

 viridis and the forms regarded as its derivatives all main- 

 tain the distance from other species, which entitled it to 

 specific rank, then the inference is justified that the 

 mutating species is C. viridis. If. on the other hand, 

 C. viridis or one of its so-called derivatives structurally 

 approaches or is very nearly identical with another species 

 of scale insect and this latter is an unstable species, then it 

 follows that the mutating species need not be necessarily 

 C. viridis alone, but the sjjecies with which C. viridis or 

 one of its derivatives is found to closely agree. 



We have now to see which of these alternatives has 

 application in regard to the variations described above. 

 The flat form from Java, the South Indian form, the 

 Coccus africanum of Uganda, are more or less referable 

 to Coccus viridis. But the round form from Java is dif- 

 ferent in structural detail. The round contour is not a 

 great difference, for it has been found occasionally among 

 the 8011th Indian forms. The eight-segmented antennae 

 are common to C. africanum and to the oval flat form 

 from Java itself. The antennae are just like those of 

 P. psidii, as will appear from the charts (PI. VII). The 

 irregularly oval approximate dermal cells and the strongly 

 developed marginal setae are peculiar to the round form, 

 which makes it structurally identical with P. psidii as it 

 occurs in Mysore. Specimens of these placed under the 

 microscope so approach each other in structure that it 

 would be difficult to tell the difference except from the 

 contour, which is round in one and oval in the other. It 

 is not known what shape P. 'psidii takes in Java, but the 

 shape is as already indicated of very little consequence. 



The structural similarity of the round form with P. 

 psidii assumes a new significance and importance when the 

 variability of Pulvinaria psidii is considered. Its varia- 

 bility is a feature of this bug which Green himself has 

 noticed both in regard to size and. anal plates. After 

 noting a minor variation in the length of the fourth segment, 

 he proceeds : " Valves of the anal operculum variable in 

 form in the same community and is particularly marked 

 in some examples from myrtle, of which no two individuals 

 are identical in this particular. . , . Length of insect 



