An aquatic Brazilian larva of the family Psychodidæ has been found by Fritz Müller to take down under the water a large bubble of air (Fig. 455, C), the main tracheal trunk ending each in an opening at the end of the body (A, B); besides this, while at the bottom it breathes by three digitiform tracheal gills; another species having two pairs (C, a).
Fig. 456.—Under side of body of larva of Blepharocera. showing the position of the tracheal gills: A, section of the body through a sucker, showing position of the gills. B, section of a sucker: br, gill with numerous tracheæ; gl, outlet of excretory gland; M, m, muscles.—After F. Müller.
The remarkable larvæ of the Blepharoceridæ (represented in the United States by Blepharocera capitata), which live permanently in swift streams, attached by median suckers to stones, are apneustic, and breathe solely by leaf-like tracheal gills (Fig. 456, br) attached to the under side of the second to sixth abdominal segments. Those of the European Liponeura are said by Wierzejski to be branched, tree-like. Also immediately in front of the anus and behind the last sucker are four membranous sacs provided with tracheæ, but which are not capable of being withdrawn. These are said by Müller to be the same as what Dewitz states to serve as gills, and by Wierzejski they are homologized with the four anal gills of Chironomus.
The double mode of respiration in the larva of the horse bot-fly has been described by Scheiber. On the hinder end of the body are the stigmatic plates, which contain two lateral gill-plates and the middle stigmatal leaf. Besides this there is a pair of slightly developed prothoracic spiracles. The embryo and also freshly hatched larva of Gastrophilus equi do not possess these gill-plates, but on the end of the body are, according to Joli, two long thread-like gills. The freshly hatched larva of the allied Cephenomyia rufibarbis bears two caudal projections. (Kolbe.) As in shrimps and other Crustacea the gills are kept in constant motion, the water being driven over them by the rapid movements of the telson, so in the larval may-flies, and in the case-worm (Macronema), the gills move more or less rapidly. In case-worms as well as larval Perlidæ, Sialidæ, Paraponyx, and Hydrophilidæ the abdominal region is constantly moved to promote respiration. (Kolbe.)
Blood-gills.—Fritz Müller describes in trichopterous larvæ certain delicate anal tubular processes into which the blood flows, and which do not as a rule contain tracheæ, though occasionally very fine tracheal branches. Müller compares them with the gills of crabs and of shrimps. They are eversible finger-like tubules. They are used when the tracheal gills are temporarily not available. Their number varies even in the same genus. There are six in certain Rhyacophilidæ; five in different Hydropsychidæ; in Macronema there are four, and they are green when filled with the green blood of that insect, the tracheal gills being whitish. In the freshly hatched larva, while the tracheal gills are present, no anal blood-gills are visible. Similar blood-gills also occur in the pupæ of certain caddis-flies. (Pictet.)
Similar anal gills filled with blood occur in the larvæ of the fireflies (Lampyris, etc.), and perhaps, Kolbe thinks, serve for respiration, though other authors believe them to be adhesive organs.
The larva of Pelobius has true blood-gills. (Schiödte. See p. 461.)
The eversible ventral segmental sacs of Scolopendrella, Campodea, and Machilis, as well as the ventral tube (collophore) of Podura, Smynthurus, etc., may, as Oudemans and Haase have suggested, serve a respiratory purpose, though they lack tracheæ, and differ from blood-gills in containing no gases; yet the blood is forced into them, causing their eversion. Oudemans observed that Machilis everted its sacs when the vessel in which it was put was filled with warm, damp air. The sacs are only thrust out when the creature is completely at rest.
Structures referable to blood-gills also occur temporarily in the embryo of Orthoptera; Rathke observed them in the mole-cricket; Ayres observed them in Œcanthus niveus, where they form two stalked broad oval appendages on the first abdominal appendages, which he regarded as gills. Patten observed them in Phyllodromia germanica, as pear-shaped structures occurring in the same situation, but regarded them as sense-organs, as did Cholodkowsky. Graber found these structures in the embryo of the May-beetle, which looked like the other embryonic limbs, but survived after the disappearance of the latter, being longer and broader and unjointed. These disappeared shortly before birth. In Hydrophilus they remain, Graber states, after birth. Nussbaum has seen them in Meloë.