DEVELOPMENT. 
217 
ure, having a very close external resemblance. Barnacles 
were long mistaken for Mollusks, Polyzoans for Polyps, 
and Lamprey-eels for Worms. Such forms are termed 
homomorphic. 
Members of one group often put on the outward ap¬ 
pearance of allied species in the same locality: this is 
called mimicry. “ They appear like actors or masquerad¬ 
ers dressed up and painted for amusement, or like swin¬ 
dlers endeavoring to pass themselves off for well-known 
and respectable members of society.” Thus, certain Butter¬ 
flies on the Amazons have such a strong odor that the Birds 
let them alone; and Butterflies of another family in the 
same region have assumed for protection the same form and 
color of wing, but lack the odor. So we have bee-like Moths, 
beetle-like Crickets, wasp-like Flies, and ant-like Spiders; 
harmless and venomous Snakes copying each other, and 
Orioles departing from their usual gay coloring to imi¬ 
tate the plumage, flight, and voice of quite another style 
of Birds. The species which are imitated are much more 
abundant than those which mimic them. There is also a 
general harmony between the colors of an animal and 
those of its habitation. We have the white Polar Bear, 
the sand-colored Camel, and the dusky Twilight-moths. 
There are Birds and Reptiles so tinted and mottled as ex¬ 
actly to match the rock, or ground, or bark of a tree they 
frequent; and there are Insects rightly named “ Walking- 
sticks” and “ Walking-leaves.” These coincidences are 
not always accidental, but often intentional on the part of 
nature, for the benefit of the imitating species. Gener¬ 
ally, they wear the livery of those they live on, or ape 
the forms more favored than themselves. 
5. Homology , Analogy , and Correlation. 
The tendency to repetition in the development of ani¬ 
mals leads to some remarkable affinities. Parts or organs, 
