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 
