188 PHYSIOLOGY OF INSECTS. 



above it, which cavity exactly corresponds, except in its 

 being somewhat deeper and more pointed, to what is called 

 the eye of a pear : twelve pears thus placed in a line, each 

 closely touching the one above it, would give a general 

 idea of the twelve corcula. Each corculnm has a most 

 distinct, tough and elastic coat, like that of an artery ; the 

 interior appears to be wholly filled with blood. The aper- 

 tures of each corculum are two, one of them at each ex- 

 tremity; the posterior aperture is occasioned by the 

 pressure of blood from below, causing the point of the 

 corculum to open : the aperture itself is surrounded by an 

 elastic ring, which expands and closes with each pulsation. 



Mr. Bowerbank, who has paid great attention to this 

 highly interesting branch of insect physiology, and whose 

 observations have been attested by the author, has described 

 in the 'Entomological Magazine' (Vol. I., p. 239), the 

 phenomena of the circulation of blood, in nearly the 

 following words. 



" The great dorsal vessel extends nearly the whole length 

 of the body, and is of great comparative magnitude. It is 

 furnished, at regular intervals, with double valves, about 

 equal in number to the sections of the body. Both above 

 and below each of these sets of valves is a pair of singular 

 looking appendages. They are probably nervous gang- 

 lions, auxiliary to the motions of the vessel, but so exceed- 

 ingly pellucid as scarcely to be defined with the highest 

 power which can be applied to them. The action of the 

 valves is a most interesting and beautiful sight. While in 

 their greatest state of collapse, the point of the lower valve 

 is seen closely compressed within the upper one. At the 

 commencement of the expansion of the artery, the blood 

 is seen flowing in from the lateral apertures, and, at the 

 same time, the stream in the artery commences its ascent. 

 When it has nearly attained its greatest state of expansion, 



