Flemiptera-Heteroptera. 5 
Ranatra the body terminates in a long breathing tube, 
and the tracheary system in these two genera is very pe- 
culiar, being very largely developed; on the underside of the 
body there is a large air-bladder within the metathorax, lead- 
ing from the spiracle, which evidently lightens the insect 
during its flicht. In the abdomen the spiracles are only 
present on the third to the fifth rings; they are not, how- 
ever, simple clefts in the wall of the body, but are closed 
by a sieve-like membrane, so that they perform the function 
of tracheal gills (Gerstaecker).” (Packard, “‘ Guide Study 
Ent.,”’ p. 537.) 
The Reproductive System.—The male generative organs 
consist of the testes, the spermatic ducts, the seminal 
vessels, and ejaculatory duct terminating in the penis; the 
female organs being the ovaries, the oviduct and sperma- 
theca and ejaculatory ducts terminating in the orifice of the 
vagina, ‘The secondary sexual organs, or armature, will be 
considered under the head of external anatomy. 
EXxTeRNAL ANATOMY. 
The Head.—Vhis varies considerably in form, but not so 
much as in the Coleoptera; the face is horizontal or 
slightly declivous in most of our species, but in the water- 
bugs and a few others it is perpendicular, or even at an 
acute angle to the vertex, as in Corixa, etc.; in shape it is 
generally more or less triangular looked at from above, with 
the eyes contiguous to or near the anterior margin of the pro- 
thorax. Notable exceptions, however, frequently occur, such 
as may be found in the Coreide, in Limnobates, etc., in which 
the eyes are far remote from the pronotum, or where the tri- 
angular shape of the head is hardly maintained, as in some of 
the Pentatomide and in the water-bugs of the genus Corixa 
Notonecta, etc., where the triangular face points downwards. 
The compound eyes are lateral and vary much in size 
and in shape; as a rule they are round and only slightly 
