182 BOWERBANK ON THE 



to the distal point of the wing, where it was discharged into the 

 great incurrent canal C, which, as may be seen in the figure, 

 passes in one unbroken line from the distal extremity of the 

 wing, until it arrives at the point D, near the proximal extremity, 

 where it divides into two branches before entering the body of 

 the insect. This canal I believe to be the only incurrent one in 

 the wing, as upon a careful examination of the canals EFGH, 

 Fig. 1, near their origin, I perceived at each spot, where an 

 arrow is placed, the globules flowing in the direction to which 

 they point, pursuing their course in a direct line along them, 

 as indicated by the straight arrows, or quitting the larger ones, 

 and passing, as indicated by the curved arrows 1 1 1 1, Fig. 1, 

 into the small lateral branches. In a similar manner I saw the 

 globules quit the large canal B, and flow in the direction of the 

 curved arrows at Fig. I, a a, through the small branches b c; 

 and in many other cases I detected single globules struggling 

 through these small transverse canals, sometimes gliding slowly 

 forward, while at other times they were stationary for a con- 

 siderable period, but always while in motion progressing towards 

 the incurrent canal C. In the upper marginal canal 7, marked 

 with double-headed arrows, the blood oscillated so continually 

 and equably, that I could not determine from the motion of the 

 globules its proper direction ; but from its position, and the 

 direction of the lateral canals connecting it with the great one 

 B, I think I may be warranted in considering it as an ex- 

 current one, particularly as the quantity and character of the 

 motion of the blood contained in it differed so materially from 

 that in the canal C, for while the motion of the blood was of 

 such an indeterminate character in the former, it was rushing 

 steadily through the latter with a rapidity greatly superior to 

 that of any other canal, and this we may conclude would naturally 

 be the case, as the canal C appears to be the sole incurrent 

 canal for the whole of the blood flowing through the two large 

 canals A B and their branches. 



The blood in its progress through the principal canals, A 

 and B, presents some singular features. While it was flowing 

 in a steady, continuous stream in the latter, it frequently 

 occurred that it would either ebb with considerable rapidity in 

 the former, for several seconds, or in the place of ebbing, 

 would oscillate for a similar period, and then resume its natural 

 course towards the distal extremity of the wing, but its velo- 

 city at no time appeared to be quite equal to that in the canal 



