no 



ENTOMOLOGY 



an inner membrane, or sarcolemma, and an outer layer of elastic con- 

 nective tissue, the adventitia. 



Pericardial Cells. Nephrocytes. The ^pericardial cells occur gener- 

 ally in larvae and imagines in the vicinity of the heart, usually on each 

 side of the heart, and arranged frequently in longitudinal " garland-like" 



FIG. 161. Diagram of a portion of the 

 heart of a dragon fly nymph, Epitheca. 

 o, ostium; v, valve; the arrows indicate 

 the course of the blood. After KOLBE. 



FIG. 162. Diagrammatic cross-section of 

 pericardial region of a grasshopper, CEdipoda. 

 a, alary muscle; d, dorsal vessel; s, suspensory 

 muscles; sp, septum. After GRABER. . 



series. They vary greatly in position, number, form, size and contents, 

 and evidently bear some relation to the circulatory system; though 

 many functions have been assigned to them. In allusion to their 

 supposed excretory function, these cells have been named nephrocytes, 

 the term applying particularly to such cells as select and absorb acid 

 ammonia carmine, when that stain is injected into the living insect. 



Ventral Sinus. In many if not most insects a pulsatory septum 

 (Fig. 1 80, v) extends across the floor of the body cavity to form a sinus, 



g 



FIG. 163. Blood corpuscles of a grasshopper, Stenobothrus. af, corpuscles covered 

 with fat-globules; g, corpuscle after treatment with glycerine, showing nucleus. After 

 GRABER. 



in which the blood flows backward, bathing the ventral nerve cord as it 

 goes. This ventral sinus supplements the heart in a minor way, as do 

 also the local pulsatory sacs which have been discovered in the legs 

 of aquatic Hemiptera and the head of Orthoptera. 



Blood. The blood, or hcemolymph, of an insect consists chiefly of a 

 watery fluid, or plasma, which contains corpuscles or leucocytes. Though 



