CIRCULATORY SYSTEM. 



313 



fices opening into each side of the dorsal vessel, and fur- 

 nished with valves. 



The dorsal vessel 

 consists, according to 

 Strauss-Diirckheim, of 

 eight successive cham- 

 bers in the cockcha- 

 fer. Mr. Bowerbank 

 says, " they are about 

 equal in number to 

 the sections of the 

 body" in the larva of 

 an Ephemera, sepa- 

 rated by converging 

 valves, which allow 

 the blood to be pro- 

 pelled forward towards 

 the head, but prevent 

 its returning. The 

 blood abounds in very 

 minute oat-shaped par- 

 ticles, and is seen cir- 

 Bating in every part 

 of the body, from 

 whence, upon each 

 pulsation and opening of the lateral apertures, it rushes 

 into the dorsal vessel, and is conveyed into the anterior 

 part of the body. When the terminal chamber is filled, 

 the blood which it contains causes the lateral valves to close, 

 and the blood to be propelled into the next chamber, which, 

 at the same time, also receives a flow of blood from its own 

 lateral openings. In this manner the blood is forced 

 towards the prothoracic chamber, where it terminates, ac- 

 cording to Strauss-Diirckheim, in a single artery, without 





