TRACHEATA 327 
union give off a trachea to the generative organs. Each of the 
dorsal loops of the system thus formed breaks up into six or 
eight smaller tracheae, which pass dorsally, giving off fine 
branches to the various viscera, and frequently terminating in 
vesicles ; the ventral loops also give off smaller branches, and 
each of the last six gives rise to a long trachea, which passes 
backward and opens into a large swelling in the fifth abdom- 
inal segment; similar branches come from both sides of the 
body, thus the right and left tracheal system is in communi- 
eation within the body. 
Each trachea consists of a tube of very thin transparent 
chitin, which is strengthened and kept expanded by a spiral 
thickening of the chitin; this gives the trachea its character- 
istic spiral appearance. The chitin is secreted by a layer of 
polygonal cells, with conspicuous nuclei, which surround the 
tracheae. The vesicles are simply oval swellings on the 
tracheae. The finest branches ramify between the cells which 
compose the various tissues, and thus in a tracheate animal 
the cells are directly supplied with air, and are not dependent 
upon the blood for their supply of oxygen. Owing to the 
complete intercommunication of the various tracheae the whole 
system could be filled with air from any one stigma, so that 
if anything rendered the supply from some of them inefficient, 
it could be made right by the others. The vesicles when 
charged with air doubtless serve to render the body of the 
beetle lighter during flight. 
The heart of the cockchafer les in the median line immedi- 
ately beneath the dorsal integument; it consists of a tube 
closed behind but open in front, with contractile muscular 
walls. In the abdominal section of this tube there are eight 
pairs of ostia, with valvular lips; through these the blood enters 
the heart, and by its contractions is propelled forwards. The 
ostia mark the hmits of the eight chambers into which the 
heart is sometimes said to be divided ; anteriorly it is continued 
into a vessel, the so-called aorta, which passes as far forward 
as the head and then suddenly ends with an open mouth. 
The heart is lodged in a space, the pericardium, whose dorsal 
wall is formed by the terga of the various seements, and the 
ventral by a pericardium or pericardial membrane. The alary 
