158 PHYSIOLOGY OF THE INVERTEBRATA. 



the alimentary canal or any secretions. As the blood in 

 Lepidopterous larv^ exists under considerable pressure, it is 

 readily obtained by making a minute prick in the hypodermis. 

 In larvae, Mr. Poulton generally pricked the distal parts of 

 the claspers ; and then examined a drop of the blood under 

 the microscope to see if any food particles were mixed with 

 it. The blood should be perfectly clear, containing only 

 colourless corpuscles, fat-cells, and minute spherules of fat. 



The blood of pupae was obtained by making a prick in the 

 cuticle of the wings. The blood at once issues, being under 

 considerable pressure. " The whole of the blood was obtained 

 by pushing the abdominal segments inwards, and ultimately 

 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 appear- 

 ance 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. The blood is received into 

 sections of glass tabes of various lengths, with the ends care- 

 fully 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 pre- 

 pared will keep for months without change. If, however, 

 air be admitted, an opaque black clot is formed on the sur- 

 face, and the rest of the blood becomes cloudy. It will also 

 keep indefinitely in sealed tubes." * 



Mr. Poulton has examined the blood of the larvae of 

 PhlogopJiora meticulosa. These larvae assume various shades 

 of colour between green and brown. The green blood was 

 taken up by a capillary tube (0.75 mm. internal diameter) ; 

 and allowed to stand four days, during which time it was 

 reduced to about half its volume (due to evaporation). The 

 tube was then sealed. The spectrum produced by using a 

 I *_Proc. Boy. Soc, vol. 38, p. 283. 



