MYRIAPODS. 



573 



without a flaw anywhere. The tubes are composed of an outer and an 

 inner coat, containing between them the spiral coil, to which they are 

 closely attached ; a delicate membrane also connects the turns of the 

 spiral* with each other. It is interesting to compare these animal 

 breathing tubes with their analogues the spiral vessels of the vegetable 

 kino-dom ; the latter are easily extracted 

 from the young shoots of asparagus, or 

 from the leaves of the hyacinth. The 

 spring-like coil insures a free open passage 

 for the air which rushes in by the spiracular 

 orifices, expiration being effected by the 

 contraction of these elastic channels, by 

 which the effete air is forcibly expelled 

 through the openings by which it origi- 

 nally entered. 



The main tracheae pass down the axes 

 of the blood-channels, floating in the vital 

 fluid, which they revivify with the oxygen 

 which they thus carry to and through the 

 life-stream. We are told that the air-pipe 

 does not terminate where the wiry-looking 

 spiral comes to an end ; the latter dwin- 

 dles away imperceptibly to nothing, but 

 the trachea thence becomes membranous, 

 and, dividing into innumerable branches, 

 which bear to the main trunks the same 

 relations that the capillaries bear to the 

 arteries, penetrates the substance of the 

 muscles, inconceivably fine branches hav- 

 ing been traced accompanying the nerves, 

 while the ultimate plexiform extremes of 

 the system aerate immediately the solids. 

 "In all the transparent structures of in- 

 sects every observer may prove for him- 

 self that the blood-currents travel in the 

 same passages as the tracheae, but this 

 is only the case with the primary and 

 secondary branches, never in the capillary 

 tracheae ; the blood-corpuscles of the Myri- 

 apod exceed by several times in diameter 

 that of the extreme capillary membra- 

 nous tracheae; it is perfectly marvelous to 

 what inconceivable minuteness the air- 

 current is reduced in traveling; along these 

 tubes." "What a simple and efficient plan, what an economy of space is 

 this arrangement of tube within tube, for aerating the blood in a class 



Trachea of Geophilus Sueter- 

 RANEUS. Magnified 140 diameters. 



