326 



INSECTA. 



Fig. 163. 



ence to the accompanying figure (fig. 163), representing a magnified 

 view of the interior of a portion of the heart of the Cockchafer, as 

 depicted by the celebrated entomotomist before 

 alluded to. The organ has been divided longi- 

 tudinally, so that one-half only is represented in 

 the figure, upon a very large scale. The compart- 

 ments (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 mem- 

 branous valves, admit blood from the cavity of the 

 abdomen, but effectually prevent its return. 



(853.) Let us now consider the movements of 

 the circulating fluids produced by the contrac- 

 tions of this apparatus. The chyle or nutritive 

 material extracted by the food exudes, 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 surface 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 aper- 

 tures ; and as it cannot return through that open- 

 ing on account of the valves (c) that guard the 

 entrance, nor escape into the posterior divisions of 

 the heart by reason of the valves (d), the contrac- 

 tion 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 heart, but does not appear to be received 

 by any vessels, and therefore becomes again diffused through the body. 

 The diffused character of the circulation met with in insects may easily 

 be made a matter of observation in many of the transparent aquatic 

 Iarva3 that are readily to be met with. When any of the limbs of these 

 larvae are examined under a powerful microscope, continual currents of 

 minute oat-shaped globules are everywhere distinguishable, moving 

 slowly in little streams some passing in one direction, others in the 

 opposite : but that these streams are not contained in vascular canals is 

 quite obvious from the continual changes which occur in the course of 

 the globules ; their movements, indeed, rather resemble those of the sap 

 in Chara, and other transparent vegetables, in which the circulation of 

 that fluid is visible under a microscope. 



(854.) The organs appropriated to furnish the different secretions met 



Internal view of a por- 

 tion of the dorsal vessel 

 of a Cockchafer : aaa,bb, 

 muscular walls of the 

 compartments; d d, in- 

 tercompartmental valves ; 

 c, valve defending one of 

 the orifices communicat- 

 ing with the general cavity 

 of the abdomen. 



