134 THE COCKROACH: 



by muscular fibres, but these he could not distinctly see. The 

 tube, he says, has no single large chamber, but is formed of 

 many little hearts (corcula) leading one into another. The 

 number of these he could not certainly make out, but 

 believed that there was one to each segment of the body. 

 During contraction each chamber became more rounded, and 

 when contraction was specially energetic, the sides of the tube 

 appeared to meet at the constrictions. The flow of blood, he 

 ascertained, was forward, the rhythm not constant. No arteries 

 were seen to be given off from the heart* Swammerdam 

 thought that his injections ascertained the existence of vessels 

 branching out from the heart, f but this proved to be a mistake. 

 Lyonnet added many details of interest to what was previously 

 known. He came to the conclusion that there was no system 

 of vessels connected with the heart, and even doubted whether 

 the organ so named was in effect a heart at all. Marcel de 

 Serres maintained that it was merely the secreting organ of the 

 fat-body. Cuvier and Dufour doubted whether any circulation, 

 except of air, existed in Insects. This was the extreme point of 

 scepticism, and naturalists were drawn back from it by Herold,J 

 who repeated and confirmed the views held by the seventeenth- 

 century anatomists, and insisted upon the demonstrable fact 

 that the dorsal vessel of an Insect does actually pulsate and 

 impel a current of fluid. Carus, in 1826, saw the blood flowing 

 in definite channels in the wings, antennae, and legs. Straus- 

 Durckheim followed up this discovery by demonstrating the con- 

 tractile and valvular structures of the dorsal vessel. Blanchard 

 affirmed that a complex system of vessels accompanied the air 

 tubes throughout the body, occupying peritracheal spaces sup- 

 posed to exist between the inner and outer walls of the tracheae. 

 This peritracheal circulation has not withstood critical inquiry, 

 and it might be pronounced wholly imaginary, except for the 

 fact that air tubes and nerves are found here and there within 

 the veins of the wings of Insects. 



* Dissert, de Bornbyce, pp. 15, 1C (1660). 



f Biblia Nature, p. 410. 



J Schrift. d. Marburg. Naturf. Gesellschaft, 1823. 



See, for a full account of this discussion, MacLeod sur la Structure des 

 Trachees, et la Circulation Peritracheenne (1880). The peritracheal circulation was 

 refuted by Joly (Ann. Sci. Nat., 1849). 



