CIRCULATION OF BLOOD. 181 



was flowing towards the distal point of the wing ; at other 

 times, when it passed in the opposite direction. Occasionally, 

 two or three oscillations followed each other with considerable 

 rapidity, while at other periods the alternations were compara- 

 tively slow and irregular ; but the general average was at the 

 rate of about 20 in two minutes. Being thus foiled in deter- 

 mining the proper direction in which the blood flowed in the 

 canal B, I mounted another of the insects in a like careful man- 

 ner, and was much mortified to find the result of my second 

 examination, after several hours' careful observation, so similar 

 in every respect to the first, as to leave me still undecided as to 

 the true course of the blood in the canal B. The only certain 

 result I gained was, that the proper motion of the blood in the 

 canal A was from the proximal towards the distal extremity of 

 the wing. The weather on the following days was w^et and 

 cold, and we did not succeed in capturing any fresh insects ; 

 I therefore continued my observations on those I had remain- 

 ing, but which became so languid as to allow me to gain very 

 few fresh results, beyond that of detecting a solitary globule 

 slowly winding its way through some of the small canals of the 

 wing, near its centre ; but this was something. I now confi- 

 dently expected, if I could but secure some fresh insects, I 

 might yet succeed in satisfying my doubts, and in determining 

 the true course of the blood in the canal B, which the before- 

 mentioned circumstances had rendered very uncertain. Fortu- 

 nately, the evening of the following day produced me another 

 specimen, and I addressed myself to the task of preparing it 

 for observation, and profiting by my previous failures ; after 

 having fixed the back of its head, thorax, and abdomen, firmly 

 to the glass, I separated the under wings just so far from the 

 body as to allow me to see distinctly the whole of their surface, 

 slightly fixing them by a small speck of gum-water beneath 

 each tip — and by these means I avoided that unnatural strain 

 which was the consequence of their former position, and which 

 had been so detrimental in my former attempts. I was now 

 amply repaid for my care. I at once perceived the globules of 

 the blood flowing steadily forwards towards the distal extremity 

 of the wing, not only in the canal A, as before mentioned, but 

 also in the canal B, in which its course in my former observa- 

 tions appeared so ambiguous. I was now able clearly to trace 

 the progress of the blood in both canals, from near the proximal 



NO. II. VOL. IV. B B 



