Packard.] INSECTS OF THE POND AND STREAM. 153 
Fig. 119. 
jects for the microscope, their bodies then are so transpar¬ 
ent. Now in the young of the larger dragon flies, such as 
Diplax, Cordulia (Fig. 120), JEschna (Fig. 121), and Ma- 
cromia (Fig. 122), the 
breathing process is carried 
on within the body. The 
terminal portion of the di¬ 
gestive tract is provided 
with ridges of mucous mem¬ 
brane. Into these folds or 
ridges numerous tracheal 
twigs penetrate (Fig. 123, 
x). The water is admitted 
through the conical valves 
at the end of the body; 
there it is deprived of its 
air, which is absorbed by 
the tracheae and ejected in 
a gentle stream, or, if the Agrion and Respiratory Leaf of Larva. 
creature is startled, it is driven out as if by a force pump 
or syringe, sending the insect forward 
several times its own length. 
Returning again to the May flies, 
Walsh has described a mode of respi¬ 
ration unique in that group, but which 
reminds us of the internal lung-like 
apparatus of the larval dragon fty. 
This curious form is otherwise an ex¬ 
ception to all insects, in that its three 
thoracic rings above are, instead of 
Cordulia lateralis. being separate, consolidated into one 
plate which extends back half-way over the abdomen. Fig. 
124, hi, shows the position of the tracheal lungs in the end 
of the abdomen. We need further observations to show 
how the animal takes in and expels the water. 
25 
Fig. 120. 
