An Instance of Mutation. 143 



one form; so also Ceylon. In Uganda the two types are 

 probably fairly fixed. Java, where the types are not yet 

 fixed and where the closest approach to psidii is found, 

 seems to be the most promising field for the experimental 

 demonstration of a common origin of the various forms, 

 though it appears unlikely that Coccus colemani will be 

 produced there. 



Until these experiments are conducted in Java or else- 

 where (some of these are being attempted in Mysore). I 

 must look for confirmation of my hypothesis in facts 

 which have already been recorded by Coccidologists. 



With regard to the two genera Pulvinaria and Lecanium, 

 Green writes as follows in his book on " The Coccidae of 

 Ceylon," p. 258 : " In all purely structural characters 

 there is nothing to distinguish the members of this genus 

 (Pulvinaria) from those of Lecanium, so much so that 

 until the period of oviposition it would be impossible to 

 determine whether an individual should be placed in one 

 genus or the other," and later, on p. "21)4, when dealing 

 with P. psidii, he says, that " in its earlier stages the 

 insect bears a superficial resemblance to Lecanium (Coccus) 

 viride, from which it may be distinguished by the absence 

 of the dark intestinal loop." 



Newstead is even more emphatic. He says in his book 

 on "The Coccidae of the British Isles," that "this genus 

 comes very near to Lecanium (Coccus), and is only separable 

 from it by the formation of a cottony ovisac below and 

 behind the posterior extremity of the body of the adult 

 female at the period of parturition. . . . All the stages of 

 the male, including the glassy puparium as well as those 

 of the female up to the time of parturition, are inseparable 

 from those of Lecanium (Coccus), so that in the absence 

 of the ovisac it is quite impossible to fix this otherwise 

 conspicuous genus." The secretion of meal is found in 

 another important genus, Protopulvinaria, in which the 

 meal is smaller in quantity, but is secreted all round the 

 margin. This genus has indeed been placed by Mrs. Fernald 

 under Pulvinaria as a subgenus, and I have already referred 

 to the secretion of meal in a species belonging to Lecanium, 

 viz. L. hemisphaericum. The secretion of meal is not, 

 therefore, an exclusive feature of Pulvinaria, but is found 

 more or less in the allied genera and in Lecanium (Coccus) 

 itself. 



To turn now to the genus Pulvinaria, the variations I 



