ANATOMY AND PHYSIOLOGY 



III 



usually colorless, the plasma is sometimes yellow (Coccinellidae, 

 Meloidae), often greenish in herbivorous insects from the presence of 

 chlorophyll, and sometimes of other colors; often the blood owes its 

 hue to yellow or red drops of fat on the surface of the blood corpuscles 

 Fig. 163). 



Hsemocytes. The corpuscles or h&mocytes (leucocytes) are minute 

 nucleated cells,j6 to 30 /* in diameter, variable in form even in the same 

 species, but commonly (Fig. 163) round, oval or ovate in outline, 

 though often disk-shaped, elongate or amoeboid in form. 



Function of the Blood. The blood 

 of insects contains many substances, 

 including egg albujnm, globulin, fibrin, 

 iron, potassium and sodium (Mayer), 

 and especially such a large amount of 

 fatty material that its principal function 

 is probably one of nutrition; the blood 

 of an insect contains no red corpuscles 

 and has little or nothing to do with the 

 aeration of tissues, that function being 

 relegated to the tracheal system. 



Circulation. The course of the cir- 

 culation is evident in transparent aquatic 

 nymphs or larvae. In odonate or ephe- 

 merid nymphs, currents of blood may be 

 seen (Fig. 164) flowing" through the spaces 

 between muscles, tracheae, nerves, etc., 

 and bathing all the tissues; separate 



. 



outgoing and incoming streams may be dragon 

 distinguished in the antenme and legs; 

 the returning blood flows along the sides 



of the body and through the ventral sinus and the pericardial chamber, 

 eventually to enter the lateral ostia of the dorsal vessel. A circulation 

 of blood occurs in the wings of freshly emerged Odonata, Ephemerida, 

 Coleoptera, Lepidoptera, etc,, the currents trending along the tracheae; 

 this circulation ceases, however, with the drying of the wings. 



The chambers of the dorsal vessel expand and contract successively 

 from behind forward. At the expansion (diastole) of a chamber its ostia 

 open_and admit blood; at contraction (systole) the ostia close, as well as 

 the valve of the chamber next behind, while the chamber next in front 

 expands, affording the only exit for the blood. The valves close partly 

 through blood-pressure and partly by muscular action. 



FIG. 164. Diagram to indicate the 



course of the blood in the nymph of a 



fly, Epitheca. a, aorta; h, 



