PA VESIE pes ita 
a 
1884.] Anatomy and Physiology of the Family Nepide. 359 
Observations on their influence over the circulation, etc., will 
be found in the January number, 1884, of the AMERICAN NATU- 
RALIST, where my investigations and results are given, that lead to 
the three following conclusions on these organs: (1) They are 
separate from the muscular system of the legs ; (2) they influence 
circulation ; (3) they are automatic. 
III. THe RESPIRATORY SYSTEM. 
Connected with the respiratory system of the Nepide there is 
a breathing apparatus, which is peculiar to this family of insects. 
This characteristic consists of an anal respiratory siphon formed 
by the apposition of the grooved faces of the caudal sete. Some 
aquatic larva have an analogous, though differently constructed 
breathing tube, which always disappears in the adult. The cau- 
dal setze of Belostoma and Perthostoma are comparatively short, 
but in Ranatra are conspicuous for their length. In breathing, 
these insects rise to the surface and thrust their respiratory siphon 
out of the water. At the bottom of this tube are two anal stig- 
Mata opening into the two main lateral trunks of the respiratory 
system, In the adult insect,the anal stigmata are the only open ones 
in the whole abdomen. In addition to these Nepa and Ranatra 
have, on the ventral surface of each of the third, fourth and fifth 
abdominal segment, two prominent stigmata, which are closed by 
à sieve-like membrane and, according to Gerstaecker, perform the 
functions of tracheary gills. 
In the adult Belostoma, the abdominal stigmata are so nearly 
obliterated that often their scars can be scarcely found with a lens; 
t the case is strikingly different in the larval forms, which have 
5X prominent stigmata on the last five ventral segments. The 
ist abdominal segment bears two pairs, and each of the four fol- 
Wing, 
one pair each. T noticed in some cases, a spot on the 
oe between the first abdominal segment and the meso- 
orax, which is, perhaps, an additional stigmata, though the work 
a this point is not very definite. The stigmata show a vestibule 
" cross section, and lie in a hairy track with their openings 
guarded by hairs. 
Tite chief external differences between the abdomen of the 
and of the adult Belostoma may be summed up as follows: 
ie m ventral surface is covered with rather coarse hairs, 
Surface smooth, the stigmata prominent and all open, 
