The ovaries in the female butterfly are sometimes so large as to crowd the other organs in the abdominal cavity. They communicate by means of tubes called oviducts with the copulatory apparatus at the end of the abdomen. The testes of the male butterfly are usually combined into a single organ; they discharge the seminal fluid into the vas deferens, whence it is conducted to a sort of pouch near the penultimate segment of the abdomen. In copulation the ends of the male and female abdomens are locked together by certain clasping appendages, and the seminal fluid of the male is forced into the body of the female, where it meets and fertilizes the eggs as they descend from the ovaries.
CHAPTER III
BUTTERFLY METAMORPHOSIS
Some insects, grasshoppers for example, pass through an incomplete metamorphosis; that is, the young grasshopper is very much like its parents except as regards size. This is the same sort of development found among birds, reptiles, and other vertebrates. The egg of a butterfly, however, does not hatch into a miniature replica of its parents, but into an altogether different sort of creature, which must pass through a complete metamorphosis before it becomes a butterfly. To put the matter briefly, there are four distinct stages in the life of a butterfly: the egg, the caterpillar, the chrysalis, and the imago, or butterfly proper.
THE FIRST STAGE OR EGG
Female butterflies are equipped with organs called ovaries which produce ova, and male butterflies have testes which produce sperm. By an act called copulation (in which the male and female abdomens are locked together by appropriate appendages) the sperm of the male is introduced into the body of the female. A single spermatozoon fuses with each ovum, and the result is a fertilized egg. The female deposits the egg upon a green leaf, and as a rule each species is limited to one or two particular kinds of plants. Butterfly eggs are small, but always large enough to be seen with the naked eye, and they vary widely in shape and color as well as in size.
THE SECOND OR LARVAL STAGE
Most butterfly eggs hatch within a week or two, producing worm-like larvae called caterpillars, which differ in appearance according to the species, but whose general characteristics are well known. The principal business of a caterpillar is to eat; no sooner has it emerged from the egg than it devours the egg-shell, and then sets to work on the leaves of the food plant. Its growth is so rapid that the outer skin must soon be shed, and this shedding process is known as moulting. Most caterpillars moult about four times. The caterpillar stage usually lasts only a month or so, but there are a few species which hibernate and spend the winter as caterpillars.
Fig. II.—The Viceroy (Basilarchia disippus), an example of the family Nymphalidae, or four-footed butterflies. This is the butterfly that mimics the Monarch; see section on Protective Mimicry. A, egg; B, caterpillar; C, chrysalis; D, imago.