CIRCULATION OF BLOOD. 185 



I did not succeed in tracing any branch of the trachea, neither 

 could I in any part of the incurrent canal C, although I 

 could readily perceive the terminations of these vessels in the 

 canal B, where it enters the incurrent one C, and of the 

 branches which run down the small transverse canals, and dis- 

 charge their contents into it throughout its whole course. 



The trachea?, in their passage through the large canals, 

 seldom pursue a straight course, but run in a serpentine direc- 

 tion, as represented at B, Fig. 2, through the space con- 

 taining them, and frequently at the spots where they give off 

 branches to supply the transverse canals, they curve so much as 

 to drop in the form of a loop within its mouth, as at Fig. 3, 

 e f, which is a magnified representation ofef, canal K, Fig. 1, 

 and likewise as at o, Fig. 4, which is an enlarged view of the 

 transverse canal h g, connecting canals F and C, Fig. 1 . 



During the course of these observations, I have used every 

 endeavour to discover, if possible, whether the blood had 

 proper vessels, or only occupied the internal cavity of the 

 canals ; the latter I am convinced is the case, as I could fre- 

 quently perceive the particles not only surrounding all parts of 

 the tracheae, and occupying the whole of the internal dia- 

 meter of the canals, but it frequently happened that globules 

 experienced a momentary stoppage in their progress, occasioned 

 by their friction against the curved surface of the tracheae, 

 which sometimes gave them a rotatory motion. 



I'HE DULL IXN LURCH WOOD CORNER. 



