1885.] Colouring of Phytophagous Larvce. 283 



tive tract. If the digestive tract had accidentally broken, fragments 

 of the food would have been found in the blood when examined 

 under the microscope, whereas it was always perfectly clear, con- 

 taining only colourless corpuscles, fat-cells, and minute spherules of fat, 

 which gradually came to the surface. Pupae were generally pricked 

 through the cuticle of the wings, and here also a considerable quan- 

 tity of blood emerged under pressure. The whole of the blood was 

 obtained by pushing the abdominal segments inwards, and ulti- 

 mately by gradually increasing compression of the pupa. Owing to 

 histolytic changes, the weak and thin-walled digestive tract is 

 broken, and a red fluid escapes, which is mixed with the last of the 

 blood. By carefully watching for the first appearance of the red fluid, 

 the blood may be obtained in a perfectly pure state, exactly resembling 

 that of the larva in clearness and in microscopic contents. A con- 

 siderable quantity of gas also emerges usually just before the ap- 

 pearance of the fluid contents of the digestive tract, from which the 

 gas also probably comes. The blood is received into sections of glass 

 tubes of various lengths, with the ends carefully ground. One end 

 is cemented with Dammar varnish to a glass slide, and when the tube 

 is filled with blood a cover- glass is placed upon the open end, and 

 becomes fixed by the drying of the blood. In most cases the blood 

 so prepared will keep for months without change. If, however, air 

 be admitted, an opaque black clot is formed on the surface, and the 

 rest of the blood becomes cloudy. It will also keep, I believe, in- 

 definitely in sealed tubes. 



The Spectrum of Unaltered Blood. — (a.) Larvce of P. Meticulosa. — 

 These larvae were very suitable for investigation, as all varieties of 

 colour between green and brown are common. The blood of a green 

 larva was taken up (December 12th, 1884) by a capillary tube with an 

 internal diameter of about '75 mm. The blood was allowed to stand 

 four days, during which it evaporated to about half its bulk, but did not 

 otherwise change ; the tube was then sealed up. The colour was bright 

 green, becoming darker after concentration. The spectrum was care- 

 fully noted (December 29th, 1884), a paraffin lamp being used. There 

 was a broad band in the red, of which the extreme edges extended 

 from 64*5 — 68"5, and when this band was best seen the violet end was 

 cut off at 51, and the green was darkened to 52. There was no ab- 

 sorption of the red end. When the blood was fresh (December 12th, 

 1884) and less concentrated, the blue came through on the violet side 

 of the darkening at 51, thus showing a broad dark band between this 

 part and the green. A more concentrated sample of similar blood, pre- 

 pared in the same way and at the same time, gave a darker band in 

 the red with the same limits but with more defined edges. The violet 

 end was similarly absorbed. There were indistinct traces of a broad 

 dim band about 59 — 61'5. 



