Fig. 434.—End of the body of the same larva as in Fig. 431, seen from the side, the branches of the main tracheæ (htr) omitted: kbl, excrementitial pellet in rectum; kb, tracheal gills; b, funnel of the closing apparatus; hz, hollow tooth of the closing apparatus; k1, k2, k3, siphonal lobes; th, tactile hair; as, chitinous plate; str, rudder; l, its thickened edge; sch, its shank; z′, z″, bristles.—This and Fig. 433, after Raschke.
Eaton states that there is a rectal respiration in the nymphs of may-flies, and Palmén observed in young larvæ of Bætis and Cloëon that the rectum took in “by gulps” water colored by carmine and expelled the whole of it at once, in order to fill it again in the same way. “This rectal respiration therefore corresponds to that of Libellulid larvæ.”
Fig. 435.—Thorax and anterior abdominal segments of the nymph of a may-fly (Cloëon dimidiatum) with tracheal gills (tk1, tk2, tk3) and the rudiments of the fore wings (VF) and hind wing (HF): tl, tracheal longitudinal trunks.—After Graber, from Lang.
Fig. 436.—Gills on the middle abdominal segments of larva of Bætis binoculatus: trl, longitudinal tracheal trunks; vf, stigmatic cord; ktr, gill-tracheæ; trk, tracheal gills.—After Palmén, from Lang.
Besides breathing by spiracles, by tracheal gills, as well as through the integument, the larva of Culex has been observed by Raschke to have a rectal respiration. At the anterior end of the rectum arises a countless number of fine tracheæ, which pass through the walls and, subdividing, end in numberless very fine twigs in the papilla-like folds situated within the rectum. The supply of tracheal twigs is greatest where the papillæ are largest. (Figs. 433, 434.)
j. Tracheal gills of the larvæ of insects
In many aquatic insects respiration is carried on by tracheal gills. These are delicate, hollow, leaf-like or tubular outgrowths of the integument usually attached to the sides or end of the hind-body, and containing a trachea which usually sends off numerous minute branches, so that the exchange of gases readily takes place in them.
