314 



ANIMALS IN INLAND WATERS 





A unique method of stabilization in running waters is the weighting 

 down of the body. In a few species of caddis worms (Gocra, Silo, Fig. 

 88) the larvae fasten larger stones to their cases, at the same time 

 providing for a smooth attachment to the substratum by means of a 

 level under surface of the stones and by filling in the cracks. Many 

 fishes of mountain streams are adapted to life on the bottom by loss 

 of the swim bladder, as in Cottus and the darters (Etheostominae) ; or 

 only a small swim bladder remains, surrounded by a capsule of bone, 



Fig. 89 Fig. 90 



Fig. 89. — Dipterous larvae from swift streams, from beneath, to show their 

 sucking disks: left, Liponeura brevirostris, a blepharocerid, after Brauer; right, 

 Pericoma calijornica, a psychodid. After Wesenberg Lund. 

 Fig. 90. — Sucking mouth of the armored catfish Placostomus sp., from swift water, 

 about twice natural size. After Rauther. 



as in the Eurasian Cobitidae and the East Indian Homaloptera. The 

 lungless mountain stream salamanders of North America (Pletho- 

 dontidae) apparently present a parallel adaptation, since other families 

 of salamanders also have a few lungless mountain brook forms. 10 



Organs of attachment of the most diverse kinds are especially char- 

 acteristic of the animals of this environment. The claws of the legs of 

 all water mites and insect larvae are strongly developed. Flatworms, 

 may-fly nymphs, and snails have adherent surfaces, which are much 

 larger in the snails of this region than they are in land snails of equal 

 size. The leeches attach themselves by means of sucking cups, the 

 posterior end of the larva of Melusina, a biting gnat, bears sucking 

 plates whose power of attachment is increased by bristles, and on the 

 flat, sole-like under surface of the larvae of other midges of the fam- 



