180 BOWERBANK ON THE 



terminated my expectations for that evening. But I had seen 

 enough to assure me that I might now, with every reasonable 

 prospect of success, expect to attain the long wished-for object 

 of my researches ; I mean, a vie.v of the course of the circula- 

 tion in the adult insect. On the following day I was fortunate 

 enough to procure several specimens of C. perla. I immediately 

 commenced upon one of these, by fixing it with a little thick 

 gum-water upon its back, upon a small slip of glass, and having 

 extended its wings as nearly at right angles to its body as I 

 could place them, I retained them in this position by a small 

 drop of gum-water under the tip of each, leaving the intermedi- 

 ate spaces of the wings quite free. I am thus particular in the 

 description of my proceedings, as it will be seen hereafter that 

 my great care in thus stretching the wings was most probably 

 the occasion of much vexation and loss of time. When I sat 

 down to the instrument, I was gratified beyond measure by 

 seeing the particles of the blood flowing with considerable 

 rapidity from the proximal end of the wing towards its opposite 

 extremity, through the large canal A, and with equal rapidity 

 through the canal B, from the distal point of the wing towards 

 the proximal ; and was congratulating myself upon having the 

 satisfaction of observing, at one view, the course of the circula- 

 tion through canals, which might be considered as equivalent to 

 artery and vein, when all at once, to my great surprise, the 

 blood in the supposed vein B commenced flowing in the oppo- 

 site direction ; while that in the canal A was stationary for 

 several seconds, and then again flowed forward in the same 

 direction as before, at the same time a series of oscillations, of 

 a very singular description, took place in the canal B. I must 

 here state, that the power used in making these observations 

 was 230 linear, and the field of view was equal to ^ of an 

 inch in diameter. In this exceedingly minute portion of the 

 canal B, a number of oscillations of the same globules occurred, 

 in one instance for 21 times, before I lost sight of them, in 

 consequence of the struggling of the insect giving fresh impetus 

 to the blood. In another instance, 84 oscillations took place 

 before the group of globules, upon which my eye was fixed, 

 quitted the field of the microscope. These oscillations seldom 

 exceeded half the length of the field, or ^ of an inch, and 

 were extremely irregular in the time of their occurrence ; some- 

 times the motion of the globules was most rapid when the blood 



