. Elements of comparative anatomy. Anatomy, Comparative. 290 COMPAR AT I YE ANATOMY. form tufts, or lamella?, which, beset the abdomen in the Ephemerida and Perlida (Fig. 151, A), or even form a tuft on the thorax (Perlida). Vague dermal respiration is here localised in definite organs. There is a larger surface in the tufted form, but this is compensated for, in the lamellar form, by the movements of the lamellae, and the consequent increase of rapidity a. in excnanging the water. When tra- cheal branches are developed in the hind gut, this region be- comes respiratory in function. Respiratio
. Elements of comparative anatomy. Anatomy, Comparative. 290 COMPAR AT I YE ANATOMY. form tufts, or lamella?, which, beset the abdomen in the Ephemerida and Perlida (Fig. 151, A), or even form a tuft on the thorax (Perlida). Vague dermal respiration is here localised in definite organs. There is a larger surface in the tufted form, but this is compensated for, in the lamellar form, by the movements of the lamellae, and the consequent increase of rapidity a. in excnanging the water. When tra- cheal branches are developed in the hind gut, this region be- comes respiratory in function. Respiration seems to be partly effected in the same region in the larva? of the Ephemerida and Perlida, although there are no special organs developed; for they have been ob- served to take water into the hind - gut. This function is more evident when the sur- face is increased in extent, as it is in the larva) of the Libellu- lida?, by the develop- ment of a large number of lamellae, arranged in dinal rows, longitudinal (Fig. 151, B off branches longitu Two trunks a) give at their Fig. 151. A Hinder portion of the body of the larva of Ephemera vulgata. a Longitudinal tracheal trunks, b Enteric canal, c Tracheal gills, d Feathered appendage to the tail. B Larva of J]schna graudis. a Superior longitudinal tracheal trunks, b Their an- terior end. c Posterior portion, branching on the hind-gut. o Eyes. The middle figure represents the enteric canal of the same larva, seen from the side. d Inferior lateral tracheal trunk, e Communication with the upper trunk, a b c as in J? (after Suckow). hinder end (c) to the hind-gut, and form a close plexus of trachea? in its lamellae. These internal tracheal gills are constantly bathed with water, owing to the movements of a valvular arrangement at the anus. In these forms therefore the hind-gut functions as a respiratory organ, just as it does in many other divisions. Palmen, J. A., Zur Morphologic des Tracheensystoms. Helsingfors, 1877. § 225. Among
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