PHYSIOLOGY OF INSECTS. 149 



563. To be distinctly understood, 

 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 

 corcttlum, and teli coreulum). Fig. 1 

 represents these in a state of con- 

 traction (systole). 



564. At the junction of each cor- 

 eulum with the next, are two great 

 veins ; these empty their contents into the cor- 

 eulum above them, and may be called the right 

 and left veins of that coreulum ; those represented, 

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

 eulum {parateli corcuU venw) : these have no such 

 distinct coats as those of the corcula. 



565. The posterior extremity oiFig- 

 the twelfth coreulum (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 coreulum, 

 into the twelfth, which instantly dilates. 

 Fig. 2 represents the twelfth, or upper 

 coreulum, in a state of dilatation 

 {diastole), 



566. The systole and diastole of each coreulum 

 take place alternately; so that when the whole 



