CIRCULATION. 243 



In all the species of these larvae I have yet examined, I have 

 found it as nearly similar as possible in appearance to that 

 which we observe in the Ephemera, and in some instances 

 it has afforded even more satisfactory results. The head of 

 this larva is much more transparent than that of the larva of 

 the Ephemera ; we therefore had a better view of the circula- 

 tion of the blood in the head of this insect than can possibly 

 be obtained in the other. In this object the blood is seen rush- 

 ing like a beautiful intermittent fountain towards the mouth, 

 and dividing, right and left, into two jets, a portion of each of 

 which flows within a given boundary past the back of the eye, 

 whilst the remainder winds its way through other channels, 

 deep in the side of the head, and returns again into the body. 

 The antennae of this insect also afford another beautiful 

 instance of the circulation being carried forward within well- 

 defined vessels. They are each composed of six joints, up 

 four of which the blood is seen to take its course, and turning 

 round the extremity of the fourth joint, it returns by a distinct 

 vessel into the head. 



In the leg, likewise, the circulating fluid and its vessels are 

 clearly and distinctly to be traced, even to the very extremity 

 of the tarsus, where, as in the antennae, the particles of the 

 blood are seen to descend on the one side of the leg, and, 

 turning the extreme point, to return up the contrary side to 

 the one by which they came down. 



I regret much that I have not yet had an opportunity of 

 examining the Ephemera in its perfect state ; but in two species 

 of Culex, one of which was first observed and brought to me 

 by my friend, Mr. Tulley, I have seen the great dorsal vessel 

 performing its functions in a manner similar in every respect 

 to its appearance in the larvae of Ephemera, Agrion, &c. &c. ; 

 but, from the body of the fly being more opaque than that of 

 the larvae, and nearly covered with its striated scales, neither 

 the valves nor the particles of the blood could be detected. 

 On another occasion, after having carefully cleared the wings 

 of Phlogophora meticulosa of their coloured scales, both Mr. 

 Samouelle and myself clearly saw a fluid pass down the side 

 of one of the principal ribs of the wing. We may therefore, 

 I think, fairly conclude, that the circulation is carried forward 

 in the perfect insect as well as in the larva, although, perhaps, 

 not with so much vigour as when young and growing. 



