1855.] Linnean Society. 383 



more opake than the preceding. They were but loosely attached to 

 the surface of the insect's body, and extremely delicate and fragile, 

 so that the slightest touch with the point of the finger reduced them 

 to a fine white powder, and hence was explained the fact, that the 

 leaves and branches upon which these insects occur, become com- 

 pletely whitened by a white powdery substance in the manner de- 

 scribed by Sir G. Staunton. On microscopic examination they pre- 

 sented a beautiful appearance of spiral structure. When one of the 

 appendages was compressed with care between two glass plates, and 

 examined under a power of 250 diameters, it was found to consist 

 of a mass of spiral threads, with their long axes running in the same 

 direction. The slightest friction of the surfaces of the glass plates 

 broke up these threads into fragments more or less minute, and if 

 the friction was continued, they were almost entirely converted into 

 granular matter. The threads differed from the cylinders found in 

 the crude wax of the Coccus Pela in not being tubular, and in their 

 diameter measuring on an average only -g-gV o^th of an inch, or about 

 one-half. Attempts were made to trace the mode of connexion of 

 these filaments with the insect's body, but owing to their extreme 

 delicacy and fragility this was found impossible. The integument, 

 however, to which they were attached was found to be perforated 

 by a number of circular openings, having a distinct double outline, 

 the diameter of the inner circle exactly corresponding with that of 

 one of the filaments. Hence it seemed probable that the spiral 

 threads, which were evidently a secretion, had issued from these 

 circular openings. "What was the chemical nature of this white 

 secretion ? A small portion, placed on a glass slide and melted over 

 the flame of a spirit-lamp, became a transparent, colourless drop, 

 which on cooling became opake white, and was then found to have 

 lost its original structure and to have become crystalline. The 

 crystals consisted partly of irregularly- shaped fragments, and also 

 contained, especially when the cooling had been conducted slowly, 

 acicular crystals arranged in stellate masses as in the case of the 

 two substances already described. The melting-point, as far as could 

 be ascertained with the small quantities experimented on, was 

 between 190° and 200° Fahr. The substance floated in water, and 

 was perfectly insoluble in this fluid, and but sparingly, if at all, 

 soluble in alcohol, sulphuric aether, or solution of caustic alkali, 

 whereas in naphtha it dissolved readily, as also in vegetable oils, 

 forming with the latter a white solid substance. From these cha- 

 racters there could be little doubt that the white secretion of 

 the Plata limbata was of a waxy nature, and also very similar in its 

 properties to the Chinese Insect- wax of commerce. 



