PHYSIOLOGY OF INSECTS. 149 



563. To be distinctly understood, p- ' 

 it will be necessary to select two par- 

 ticular corcula, and describe their 

 motions ; for this purpose we will 



take the two most readily observed, 

 the twelfth and thirteenth (parateli 

 corculum, and teli corculum). Fig. 1 

 represents these in a state of con- 

 traction (systole). 



564. At the junction of each cor- 

 culum with the next, are two great 



veins ; these empty their contents into the cor- 

 culum above them, and may be called the right 

 and left veins of that corculum ; those represented, 

 Fig. 1, c and d, being the veins of the twelfth cor- 

 culum (parateli corculi vence) : these have no such 

 distinct coats as those of the corcula. 



565. The posterior extremity of Fig 

 the twelfth corculum (Fig. 2, a), the 

 anterior extremity of the thirteenth 

 (Fig. 2, b), and the two veins (Fig. 



2, c and d), open simultaneously, and 

 the blood rushes upwards, both from 

 the veins and the thirteenth corculum, 

 into the twelfth, which instantly dilates. 

 Fig. 2 represents the twelfth, or upper 

 corculum, in a state of dilatation 

 (diastole). 



566. The systole and diastole of each corculum 

 take place alternately; so that when the whole 



