. Nature-study; a manual for teachers and students. Nature study. FISHES—AQUARIA 171. gills will be seen lying in several layers in the cavity. The gills are composed of small red tilaments attached to carti- laginous or bony arches. Between these arches are slits that communicate with the back part of the mouth, through which the water is forced. As the water passes over the gills, the fine blood-vessels lying in the surface of the gill filaments absorb the free oxygen in it. This is the way the fish breathes. Dissect the fish and find the air-bladder, a long, white sac in the body cavity nex
. Nature-study; a manual for teachers and students. Nature study. FISHES—AQUARIA 171. gills will be seen lying in several layers in the cavity. The gills are composed of small red tilaments attached to carti- laginous or bony arches. Between these arches are slits that communicate with the back part of the mouth, through which the water is forced. As the water passes over the gills, the fine blood-vessels lying in the surface of the gill filaments absorb the free oxygen in it. This is the way the fish breathes. Dissect the fish and find the air-bladder, a long, white sac in the body cavity next to the backbone. This organ is found in most fishes and has an important function. In fish like the sunfish, bass, and pickerel, it sen-es as a floating device. The body of the fish is slightly heavier than the water and naturally sinks. By expanding this bladder the fish can rise, and vice versa. The same jjrinciple is applied in our sub- marine boats. Watch a fish in the aquarium as it rises and sinks without moving any fins. It is done by means of the air-bladder. In the dogfish and other fishes, generally of low degree, the air-bladder serves partly as an organ of respiration. It is more or less cellular and lung-hke, and is connected with the mouth so that the fish may come to the surface and inhale air. Fishes, like amphibians and reptiles, are cold-blooded ani- .mals. That is, their blood is not, as in the birds and mam- mals, at a higher temperature than the medium around them. Flc. ,17. The a Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Holtz, Frederick Leopold, 1870-. New York, C. Scribner's Sons
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