38 



THE CLASS OF INSECTS. 



blood is accumulated about the heart and enters into it during 

 the diastole of each of its chambers, through the lateral 

 orifices (Fig. 46?)- It then passes, by the regularly successive 



FL-. -17. 



IM-. 4H. 



contractions of the heart, from behind forwards into the aorta, 

 which is only a prolongation of the anterior chamber. This 

 aorta consists of a simple, small vessel, situated on the dorsal 

 surface of the thorax (Fig. 4-4 e), and extending even to the 

 cephalic ganglion, where it either ends in an open extremity, or 

 divides into several short branches which terminate in a like 

 manner. The length of the dorsal vessel depends, in all the 

 three states of insects, upon that of the abdomen. The number 

 of its chambers is very variable, but is, most usually, eight. 



"The blood, after leaving the aorta, traverses the body in 

 currents which are also extravascular, and in this way bathes 

 all the organs. The newly-prepared nutritive fluid passes 

 through the walls of the digestive canal in which it is found, 

 into the visceral cavity, and thence directly into the blood. 

 Latterly, this extravascular circulation has been called in 

 question, but its presence may be easily and directly observed 



FIG. 40. Part of the dorsal vessel or heart of Luoums cerrns ; a, the posterior 

 chambers (the anterior chambers are covered by a part of the ligaments which hold 

 the heart in place), i, the auriculo-ventricular openings; g, f/, the lateral mus- 

 cles fixed by the prolongations li,h,tn the upper side of the abdomen. /'Vom 

 Straus Durckheim. 



FIG. 47. Interior of the dorsal vessel; a, the inner walls with their circular 

 fleshy fibres; c, the auriculo-ventriculav opening: with its semihmar valve (c), in 

 front of which is </, the interventricular valvule. From Straus Durckheim. 



