136 M. straus-durckheim's 



are far less energetic than in the warm-blooded Vertebrata, 

 for they can endure long a highly rarefied atmosphere, or even 

 irrespirable gases, without perishing. 



In Insects, the circulation having reached such a degree of 

 simplicity and imperfection, that the blood cannot be brought 

 to one special respiratory organ, this inconvenience has to be 

 remedied by replacing the circulation of blood by that of air. 

 In Vertebrata it is the blood which goes to meet the air; in 

 Insects the air seeks the blood. 



This circulation of air takes place by means of vessels called 

 irachecB, which are distributed throughout the body, after 

 the manner of the arteries of the higher animals. These 

 trachece communicate with the external air by means of certain 

 openings called stigmata, which never exceed eighteen in 

 number, placed one on each side of the jirothorax, the meso- 

 tJiorax, and the seven anterior segments of the abdomen. 

 Each of these stigmata communicates with one large, and 

 mostly very short, trachea, commonly called the primary 

 trachea {trachee crorigine), from which numerous branches 

 spread throughout the body. In some species there arise, 

 from each primary trachea from one to five branches, the 

 longitudinal trachece {tracMes de communication longitudi- 

 nale au trachees longitudinales), which run to the other 

 stigmata of the same side, to establish a communication be- 

 tween them. Other branches arise more or less directly 

 from the primary trachece, to anastomose with the trachece on 

 the opposite side ; these may be called transverse trachece 

 {trachees de coinmunicatio7i transver sales, ou trachees trans- 

 versales.) Besides these, every primary trachea sends off' in- 

 numerable branches, which, with the other branches arising from 

 the larger trunks, penetrate every part of the body. Such is the 

 distribution of the trachece in the Coleoptera and Scolopendrce. 



In other insects, as Blatta, Locusta, Sec, each primary 

 segment sends off' several trunks, some of which follow the 

 sides of the segment to which they belong, directing their 

 course towards its median line, where they open into a longi- 

 tudinal trachea, which is continued throughout the whole 

 length of the body, as well above as below. At each segment 

 these longitudinal trunks send off" a branch which anastomoses 

 with the opposite longitudinal trachea. From these different 

 trunks the smaller branches are distributed over the body. 



