NATURAL HISTORY. 23 
distinctly developed in the head, and a larger 
branch to each eye. These vessels are double, 
and each separates into two at the commence- 
ment of the second segment or mesothoraz, but 
they afterwards unite a little lower down, first 
sending out a branch to each of the middle pair 
of legs, which have their insertion in this seg- 
ment. The first pair of wings subsequently 
emanate from this part, which may account for 
the division of these vessels. The re-united 
vessels proceed onward to the posteriorextremity 
of the body, and then beautifully ramify over 
the three membraneous appendages of the tail, 
each appendage being furnished with a branch 
from both the trachee. The larva of the Ephe- 
mera marginata have a series of smaller leaf- 
like appendages, on each side of the body (see 
“Microscopic Illustrations,” fig. 7), which are 
considered to perform the office of gills. It is, 
therefore, exceedingly probable that these tails 
of the Libellula, which are similar in appearance, 
perform the same office, although they do not 
exhibit that vibratory motion which is produced 
by the ephemera. 
In the infant larva these caudal appendages 
are not developed, but consist of three tubular 
spines, with smaller ones proceeding from them. 
