184 BOWERBANK OS THE 



length, were so opaque as not to allow of their internal cavity 

 being examined, yet at their junction with the canal A they 

 were so far transparent as to allow of the branch of the trachea 

 being seen had it been present, neither did the trachea in the 

 canal A curve towards the mouths of the transverse canals, 

 as it usually does when it gives off a branch. The trachea 

 in the canal B, unlike that in canal A, pursues an exceedingly 

 tortuous course, with very little diminution in its diameter for 

 about three-fourths of its length ; it then gradually decreases in 

 size until it reaches the distal extremity of the canal B, when 

 it becomes so slender as generally to elude observation. In 

 its progress it gives off a branch to the canal E, at its origin i, 

 Fig. 1 ; which, shortly after its entrance into that canal, 

 divides into two parts ; one of these branches passes at k into 

 the canal K, Fig 1. Here the trachea is very large in propor- 

 tion to the space containing it, filling up at least three-fourths 

 or four-fifths of the cavity, and giving off small branches to 

 each of the posterior transverse canals ; which canals ap- 

 pear, in every wing I have examined, to receive the branch of 

 the trachea destined for their use from the trachea of the large 

 canal immediately above them, and in no instance that I have 

 observed from that belonging to the one beneath them. 

 These fine branches, which pass through the small trans- 

 verse canals, do not enter the trachea, which runs through the 

 large longitudinal one beneath them, but usually terminate 

 in a fine point at the spots where the transverse canals join 

 the longitudinal ones beneath ; sometimes instead of termi- 

 nating at the junction of the two they run for a short distance 

 into the large longitudinal one ; and in one instance, g, Figs. 

 4 and 1, I observed that the trachea divided at the spot where 

 it usually terminates, into two branches, which after running 

 for a short distance along the canal C, the one towards the 

 distal, and the other towards the proximal extremity of the 

 wing, then terminated in the usual manner in a fine point. 

 Generally speaking each canal contains but one branch of the 

 trachea, and in the large ones, A and B, I believe this to be 

 universally the case, but in one wing in the canal ^,IFig. 1, at 

 the point ??f, and in F, Figs. 1 and 4, at the point b, I observed 

 two branches in each, and in one instance in the latter, as 

 many as three branches ; and indeed, in this canal, the trachea 

 seems to be more subject to divide into separate branches than 

 in any other in the wing. In the upper marginal canal /, 



