CIRCULATION IN INSECTS. 241 



into the scattered streams, which descend along 

 the sides of the body, and which, after having 

 thus completed their circuit, return into the pul^ 

 sating dorsal vessel. 



This mixed kind of circulation, partly diffused 

 and partly vascular, is beautifully seen in the 

 larva of the Ephemera marginatay^ where, be- 

 sides the main current, which, after being dis- 

 charged from the anterior extremity of the dorsal 

 vessel, descends in a wide spreading stream 

 on each side and beneath that vessel, another 

 portion of the blood is conveyed by two lateral 

 trunks, which pass down each side of the body, 

 in a serpentine course, and convey it into the 

 lower extremity of the dorsal vessel, with which 

 they are continuous. These are decidedly ves- 

 sels, and not portions of the great abdominal 

 cavity, for their boundaries are clearly defined ; 

 yet they allow the blood contained in them 

 to escape into that cavity, and mix with the 

 portion previously diffused. All these wandering 

 streams sooner or later find their way into the 

 dorsal vessel ; being absorbed by it at various 

 points of its course, where its membranous coat 

 is reflected inwards to form the v^ve*. In the 



* This insect is figured and described in Dr. Goring and 

 Mr. Pritchard's " Microscopic Illustrations," and its circulation 

 is very fully detailed, and illustrated by an engraving on a large 

 scale, by Mr. Bowerbank, in the Entomological Magazme, i, 239 ; 

 plate ii. 



VOL. II. U 



