104 GENERAL ZOOLOGY 



ful. They are produced by the little scales which cover the 

 wings and other parts of the body. They may be due to 

 the presence of specific pigments which give a particular 

 tint to the surface, or they may be " refraction colors" 

 caused by the spreading of the light from the many small 

 flat surfaces presented by the scales. Reds, yellows, and 

 browns are usually pigment colors, while greens and blues 

 are more often due to refraction. 



The development of Jepidopterous insects (Fig. 51) may 

 well illustrate the holometabolous type; the monarch 

 butterfly and cecropia moth serving as examples. The 

 monarch lays its eggs in little groups on the underside of 

 milkweed leaves. These eggs produce minute larvae which 

 at once begin to feed on the leaf where they hatch. The 

 larvae grow rapidly, moulting several times, and when 

 mature measure an inch or more in length. They then 

 attach themselves in a suitable place, moult the larval skins, 

 and become naked pupae, or chrysalids, which hang sus- 

 pended until they in turn moult to become imagoes, or adult 

 butterflies. The cecropia moth lays its eggs in the spring 

 on willows, and the larvae which hatch feed voraciously on 

 the leaves. When grown each of them spins a cocoon about 

 itself and passes through the winter attached to some 

 branch, safe inside its silken covering. In the spring an 

 adult moth emerges from the pupal skin and forces its way 

 out of the cocoon. The imago of this moth never eats and 

 its mouth parts are rudimentary. Its chief work in life is 

 to find a mate and start a new generation. 



There are many butterflies of particular interest. 

 Among the most beautiful are the swallowtails (Family 

 Papilionidce) which have slender appendages from the 

 posterior portion of the wings. The mourning-cloak 

 butterfly (Euvanessa antiopa) is one of the harbingers of 

 spring in most parts of the United States. Its larva often 

 does damage to poplar and willow trees. The " monarch" 

 (Anosia plexippus) and ''viceroy" (Basilarchia archippus) 

 furnish an excellent case of mimicry. The monarch is dis- 



