CIRCULATION OF THE BLOOD. 411 



which are found in the ribs of the wings, and which we have mentioned 

 above. I detected such vessels in many insects which I then examined, 

 namely, in Dyticus marginalia, Copris lunar is, Pkilanthus pictus, &c., 

 but I yet doubt, from more recent investigations that I have made in 

 the bright and partially transparent pupae of some capricorns, namely, 

 Prionus faber and coriarius, the correctness of my above mentioned 

 opinion. In the rudimentary wings of these pupae I saw with un- 

 assisted eyes perfect tubes as silvery-white glittering filaments con- 

 taining air. These tubes in the upper wing or elytron gave off no 

 branches, but ran undivided in a direct line from the base to the apex. 

 But at the extreme base they collected into two main stems, the one 

 of which takes its course at the anterior margin, and the other upon 

 the sutural margin, both originating at the thorax as a simple stem. 

 The anterior one has two and the posterior one four straight radiating 

 branches, which run parallely. The tubes of the inferior or true wing 

 were divided, but likewise also only towards the apex. They also 

 originated from two similarly disposed main stems, the anterior one of 

 which likewise sent off two and the posterior one four branches. I 

 could distinctly see this by means of a simple lens. Upon its inspection 

 with the microscope, these tubes were observed filled with air, which was 

 interrupted at certain parts, so that the tubes appeared to contain 

 disconnected air-bladders. I could not even yet detect by means of the 

 microscope the structure of the tubes, which was only visible upon 

 removing the external tunic of the elytron, and the tube then lay 

 distinctly in the parenchyma before me ; an extremely fine filament 

 was then seen, which wound itself spirally around the circumference 

 of the tube, and left a tolerably wide space between it. On each side 

 of these tubes there was a bright stripe, as if a channel lay free in the 

 parenchyma contiguous to the trachea. I now repeated my investiga- 

 tion in other insects which had been immersed for some time in spirits 

 of wine, but I found neither in the vessels of the elytra, nor in those 

 of the wings, a spiral twisting, and just as little in dried specimens. 

 Thence I might conclude that the spiral filament becomes invisible by 

 immersion in alcohol as well as by drying in the air, at least under 

 the microscopic power that was at my command, but that it never- 

 theless existed in all the vessels that take their course through the ribs 

 of the wing ; that consequently all these vessels must absolutely be con- 

 sidered as tracheae, and that blood-vessels are not to be found even in 

 the ribs of the wings. 



