430 Mr. Newport on the Anatomy and 
and metathorax, below the second, or mesothoracic spiracles, while the other 
projects from the anterior of the metasternum. The sixth, like the fourth, is 
only a single pair of sacs in the soft membrane of the articulation of the coxe 
of the third pair of legs (4); while the seventh and eighth, also single pairs 
of sacs, project from the inferior lateral surface of the first and second ab- 
dominal segments, in situations nearly corresponding to the usual place of 
spiracles in other insects. 
M. Pictet has described the branchial tufts in the larva of Perla bipunctata 
very precisely, and has successfully combated the opinion put forth by M. Bur- 
meister, in opposition to his view, that the branchial filaments are only stiff 
hairs. A careful examination of the tufts in Pteronarcys has confirmed to 
ine the correctness of M. Pictet's observations as regards their true nature. 
Each tuft or sac (fig. 3) is an extension outwards of the soft tegument from 
which project an abundance of delicate cecal filaments. Each filament (fig. 4) 
is a simple, unarticulated, uniform structure, slightly tapering and closed at 
its extremity, and in the interior of which there is an extremely minute tra- 
cheal vessel (c). On examining some of these filaments taken from the 
branchiz of my specimen of Pteronarcys formerly, in company with Professor 
M.-Edwards, we were unable, at that time, to satisfy ourselves of their true 
branchial function; but longer-continued, repeated, and more carefully con- 
ducted investigations have now most fully satisfied me of their real import- 
ance as active organs in the imago. The uncertainty of.former examinations 
arose, as I now find, from the branchial filaments being greatly altered in 
their appearance by the contraction of their fibrinous tissue, together with the . 
coagulation of the circulatory fluid and blood-corpuscles within them, occa- 
sioned by the insect having been killed and preserved in spirits. I have 
since recognised corresponding appearances, induced by a similar cause, ,in 
the branchiz of other insects killed in like manner. | 
The number of filaments produced from each sac varies from about twenty 
to fifty pe more. It is greatest in the sacs of the meso- and metathorax, and 
cad the neck and of the abdomen. The filaments originate in 
idis or five in each, from the distal border of the sac, but not 
all On pieiaely the same line. Usually each filament is simple and distinct ; 
but in a few instances, as in some (fig. 4) from the external sac at the anterior 
