1908.] The Oyster-Shell Bark Scale. 615 



over 2 millimetres. It is round, not much raised, and smooth. 

 The central part of the scale is dark coloured, the rest being 

 yellow-brown or dark grey. Over-crowding causes considerable 

 variation in the shape of the scale. Owing to its flatness and 

 its close adherence to the bark, it may become more or less 

 incorporated with or covered by scales of the epidermis 

 of the plant or loose external matters, and thus, with a 

 colour resemblance to the bark, the scale may easily pass 

 unnoticed. 



Adult Female. — The female is flat, almost round, and yellow. 

 As adult the female is without eyes, legs and wings, and has 

 only rudimentary antennae. There is a characteristic piercing 

 and sucking mouth apparatus . The hind region of the abdomen 

 shows, under magnification with the microscope, five groups of 

 circumgenital glands, the anterior group having fewer pores 

 than the lateral groups. 



Male Scale. — The male scale or shield is small, measuring 

 only 1 m.m. ; it is rounded oval or, in other cases, elongate 

 oval. 



Adult Male. — The adult male insect is orange-yellow in 

 colour, with a dark band across the thorax. The male has 

 antennae, legs, and two wings, but no functional mouth. 



Male Pupa. — The pupa has no mouth organs, but has 

 antennae, legs, and signs of the future wings. It is yellow in 

 colour, with the eyes and ocelli, black. 



Second Stage of Male and Female. — The insect in this stage 

 is without wings or legs, being unable to move ; it remains 

 anchored to the bark by its rostrum. 



Larva. — The larva from the egg is very minute but is fairly 

 active ; a pair of 6-jointed antennae, 6 legs and sucking mouth 

 apparatus are present. 



Life History. — The winged males appear towards the end 

 of April or in May, according to the weather conditions. By 

 this time the females are adult and fertilisation takes place. 

 Eggs are laid containing larvae ready to hatch. The tiny 

 larvae wander over the bark, ultimately settling down to feed 

 by inserting into the bark their sucking mouth parts. In 

 this larval stage there is practically no sexual distinction. A 

 secretion is given off which covers the larva, and later the first 

 moult takes place and the second stage is attained. The 



