VOL. XliIV.] PHILOSOPHICAL TRANSACTIONS. 291 



then collected a great many, and put in boxes ; and by strictly observing them, 

 he could tell when they were ready to put off their old cloaths, though but so 

 lately put on. 



He had the pleasure to show his friends one that he held on his finger all the 

 while it performed this great work : it was surprising to see how easily the back 

 part of the fly split open, and produced the new birth, which he could not per- 

 ceive partakes of any thing from its parent, but leaves head, body, wings, legs, 

 and even its three-haired tail behind, or the cases of them. After it has reposed 

 itself awhile, it flies with great briskness to seek its mate. 



In the new fly a remarkable ditFerence is seen in their sexes, which he did not 

 so easily perceive in their first state, being then male and female much of a 

 size, but now the male was much the smaller, and the hairs in their tail much 

 the longer. 



He was very careful to see if he could find them engendering, conceiving it 

 to be much after the manner of the same species : but all that he could discover 

 was, that the males separated, and kept under the cover of the trees, remote 

 from the river. Hither the females resorted, and mixed with them in their 

 flight, great numbers together, with a very brisk motion, of darting or striking 

 at each other, when they met, with great vigour, like as house-flies will do in a 

 sunny room. This they continued to do for many hours, and this seemed to be 

 their way of coition ; which must be quick and soon performed, as they are of 

 so short duration. He tried several ways to make further discoveries, but all 

 proved ineffectual. 



When the females were impregnated, they soon left the company of the males, 

 and sought the rivers, and kept constantly playing up and down on the waters. 

 It was very plainly seen, every time they darted down, that they ejected a cluster 

 of eggs, which seemed a pale bluish speck, like a small drop of milk, as they 

 were sinking to the bottom of the river ; and then, by the elasticity of their tails, 

 they spring up again, and then dart down again. Thus they continue, till they 

 have exhausted their stock of eggs, and spent their strength, being so weak that 

 they can rise no more, but fall a prey to the fish. 



But by much the greater numbers perish on the waters, which are covered 

 with them. This is the end of the females ; but the males never resort to the 

 river that he could perceive ; but after they have done their office, drop down, 

 languish, and die, under the trees and bushes. 



He observed that this species of libella abounded most with females ; which 

 was very necessary, considering the many enemies they have in their short ap- 

 pearance ; for both birds and fish are very fond of them, and doubtless under the 

 water they are a food for small aquatic insects. 

 What is further remarkable in this surprising creature is, that in a life of 3 or 



p p2 



