Mr. K. Kunki Kannan on An Instance of Mutation. 131 



those between P. psidii and C. viridis, and are similarly 

 explained by the theory of regressive mutation. 



The two insects dealt with in this paper belong to two 

 closely allied genera in the order Coccidae. They are flat, 

 oval scale or scab-like bugs, which are provided with 

 hair-like tubes for feeding on plant sap. The adults show 

 little trace of segmentation. They have three pairs of 

 legs, a pair of segmented antennae, a pair of eyes, and two 

 pairs of spiracles, which are situated a little distance 

 from the margin, but are connected with it by shallow 

 grooves called stigmatic clefts. At the place where the 

 grooves touch the margin there are three stout spines, of 

 which the central spine is twice the size of the other two. 

 At short intervals along the entire margin, there are smaller 

 spines which are dilated or toothed at the extremity. 

 The anus is about a sixth of the distance from the margin, 

 and is guarded by two triangular chitinous plates known 

 as the anal plates, which lift up and open apart when there 

 is a discharge. From the anus, in a line with the opening 

 of the plates, there runs to the margin, a cleft dividing 

 the posterior end into two lobes. The chitin of the dorsum 

 has a definite pattern made up of what are called dermal 

 cells, which are depressions or pits* of different shapes 

 varying from irregularly oval to round. Coccus viridis 

 is viviparous, the eggs developing inside the body and 

 hatching usually at the time of discharge. Pulvinaria 

 psidii, on the other hand, secretes a cottony waxy stuff 

 to lay eggs in. 



Coccus viridis, or green bug, is a serious pest of Coffee, 

 which appeared in Ceylon so far back as 1882, and had no 

 small share in the destruction of Coffee there. It lias 

 since appeared in the Pulneys, the Shevroys, the Nilgris, 

 and finally in Mysore and Coorg. It feeds on a large 

 number of plants, besides Coffee, viz. Tea, Cuava, Citrus 

 plants, Cinchona, several species of Manihot, Gardenia, 

 Ixora, Plumiera, Eugenia, Loranthus, Antidesma, and 

 several varieties of garden shrubs. 



* The dermal cells cannot lie correctly described ;is "depressions 

 or pits." They are actual cells in the chitinous substance of the 

 derm, each cell communicating with the surface by a minute pore. 

 They have no connection with the superficial depressions (usually 

 of a more or less polygonal form) that may he observed on the 

 dorsum of the living insect. — E. E. G. 



