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gans of breathing have the structure of gills. In 
the fresh water muscle are two pair of gill-like la- 
mine at the mouth, and two pair on the back. In 
the gasteropoda, some respire water altogether, and 
exhibit fibrous gills, some in tufts, some in fringes. 
In helix and limax, which breathe air wholly, the 
respiratory cavity is easily distinguished. In ce- 
phalopoda, the sepiz, is a compound apparatus, a 
muscular sac receiving water to convey it to the 
gills. In the articulata are varieties of respiratory 
apparatus; bladders in the dew worm and leech; 
gills in several marine worms, spirillum, serpula, 
living in calcareous tubes; and in lumbricus mari- 
nus. In the aphrodite aculeata, the matted hair is 
connected with respiratory organs. Amongst in- 
sects, numerous larvae respire water by fibrous gills: 
some, in the perfect state, have respiratory tubes, 
as the nepa, in the form of bristles, extending back- 
wards: most breathe air through stigmata, small 
apertures on the sides of their bodies. The gills of 
the crustacea are in some external, as in squilla, 
apus, &c.; in some internal, as the crab, lobster, &c. 
«« We commonly find that some species in a given 
class or order are its proper representatives, whilst 
others may be considered rather as connecting links 
with superior and inferior formations: so in fishes, 
the abdominales, salmon, carp, pike, &c. decidedly 
present in their structure every distinctive character 
of fish; while rays and sharks approach, even in 
their respiratory organs, to the amphibia: myxines 
and lampreys to worms.” Amongst amphibia, sirens, 
