INSECT A. 



269 



sists, in the cockchafer, of eight distinct compartments, sepa- 

 rated from each other by as many valves formed by productions 

 from the lining membrane, and so disposed that the blood passes 

 freely from the hinder chambers into those which are placed more 

 anteriorly, but is prevented from returning in the opposite di- 

 rection. 



Each compartment of the dorsal vessel communicates by two 

 wide slits, likewise guarded by valves, with the cavity of the 

 belly, so that fluids derived from thence will readily pass into the 

 different chambers, but cannot .again escape through the same 

 channel. The arrangement of these valves will, however, be best 

 understood by reference to the accompanying Fig. 120. 

 figure (Jig. 120), representing a magnified view 

 of the interior of a portion of the heart of the 

 cockchafer, as depicted by the celebrated en- 

 tomotomist above alluded to. The organ has 

 been divided longitudinally, so that one half only 

 is represented in the figure upon a very large 

 scale. The compartments (a, a, a) are distinctly 

 composed of circular muscular fibres ; the large 

 valves (d, d) separate the individual chambers, 

 allowing the blood to pass in one direction only, 

 viz. towards the head ; while the openings (c), 

 likewise closed by semilunar membranous valves, 

 admit blood from the cavity of the abdomen, but 

 effectually prevent its return. 



(311.) Let us now consider the movements of 

 the circulating fluids produced by the contractions 

 of this apparatus. The chyle or nutritive material 

 extracted by the food, eludes, as we have already seen, by a species 

 of percolation through the walls of the intestine, and escapes into 

 the cavity of the abdomen, where it is mixed up with the mass of the 

 blood, which is not contained in any system of vessels, but bathes 

 the surfaces of the viscera immersed in it. When any compartment 

 of the heart relaxes, the blood rushes into it from the abdomen, 

 through the lateral valvular apertures ; and as it cannot re- 

 turn through that opening on account of the valves (c) that 

 guard the entrance, nor escape into the posterior divisions of the 

 heart by reason of the valves (c?), the contraction of the dorsal 

 vessel necessarily forces it on towards the head. When it arrives 

 there, it of course issues from the perforated termination of the 



