188 
COMPARATIVE ZOOLOGY. 
passing their antennae. All the higher animals, too, have 
similar emotions—as joy, fear, love, and anger. 
While instinct culminates in Insects, the highest devel¬ 
opment of intelligence is presented in Man. 103 In Man 
only does instinct cease to be the controlling power. He 
stands alone in having the whole of his organization con¬ 
formed to the demands of his brain; and his intelligent 
acts are characterized by the capacity for unlimited prog¬ 
ress. The brutes can be improved by domestication; 
but, left to themselves, they soon relapse into their origi¬ 
nal wildness. Civilized Man also goes back to savagery; 
yet Man (though not all Men) has the ambition to exalt 
his mental and moral nature. He has a soul, or conscious 
relation to the Infinite, which leads him to aspire after a 
lofty ideal. Only he can form abstract ideas. And, 
finally, he is a completely self-determining agent, with a 
prominent will and conscience—the highest attribute of 
the animal creation. In all this, Man differs profoundly 
from the lower forms of life. 
3. The Voices of Animals. 
Most aquatic animals are mute. Some Crabs make 
noises by rubbing their fore-legs against their carapace; 
and many Fishes produce noises in various ways, mostly 
by means of the swim-bladder. Insects are the Inverte¬ 
brates which make the most noise. Their organs are usu¬ 
ally external, while those of Vertebrates are internal. In¬ 
sects of rapid flight generally make the most noise. In 
some the noise is produced by friction (stridulation); in oth- 
ers, by the passage of air through the spiracles (humming). 
The shrill notes of Crickets and Grasshoppers are pro¬ 
duced by rubbing the wings against each other, or against 
the thighs; but the Cicada, or Harvest-fly, has a special 
apparatus—a tense membrane on the abdomen, acted upon 
by muscles. The buzzing of Flies and humming of Bees 
