THE CHARACTERISTICS OF INSECTS. 223 



THE CHARACTERISTICS OF INSECTS. 



By LOUIS MONTILLOT.* 



INSECTS, arachnids or spiders, myriapods and crustaceans, 

 are all included in the sub-branch of the arthropods or joint- 

 limbs. Of the characteristics by which they are distinguished 

 we mention here only the most salient. Insects have six legs, 

 arachnids eight, and myriapods a more considerable number, but 

 always short of ten thousand. The legs of crustaceans are vari- 

 able in number ; they have a carapace consisting of the external 

 skeleton, which, being impregnated with carbonate and phos- 

 phate of lime, is always consistent and sometimes very hard. 



The body of insects is divided into three distinct parts: the 

 head, the thorax, and the abdomen. We may therefore define 

 insects as articulated animals with six legs, having head, thorax, 

 and abdomen distinct. 



The life of the insect comprises four successive stages : those 

 of the egg, the larva, the pupa, and the perfect insect. The rule, 

 however, is subject to some interesting exceptions. The repro- 

 duction of insects usually takes place through sexual connection. 

 The eggs are fertilized while passing through the oviduct of the 

 female ; but the females of certain bees, some of the butterflies, 

 and several aphides, lay fertile eggs without the assistance of the 

 male ; this phenomenon is known as parthenogenesis. With some 

 other species the females are viviparous. 



The egg is composed of a firm shell, containing a limpid liquid 

 that includes the germ of the embryo and the vitelline globules 

 which are destined to nourish it. The eggs of insects are of the 

 most diversified forms. The shells of many are adorned with 

 remarkable figures. At the moment of hatching, the shell breaks, 

 or rather opens like a hinged box-cover. A large number of the 

 eggs look like seeds. Some are round, others cylindrical, conical, 

 or hemispherical. Others represent solid forms, either flattened or 

 terminating in a point. A curious study is furnished by the art 

 with which the females deposit their eggs. Here we find single 

 eggs ; there we see them collected in considerable numbers within 

 a parchment or silken protective envelope, which floats on the 

 water, or is inserted in bark or attached to a stone. At other 

 times we find a chaplet of symmetrical beads, arranged in 

 closed rings around the branch of a tree. To deposit her eggs, 

 the female bores with her ovipositor into the stems of plants, the 

 tissues of animals, or the timbers of our houses. There are no old 

 tree-trunks or cracked walls that may not serve her for a hatch- 



* Translated from the book L'Amateur d'Insects. Paris: J. B. Bailliere et fils, 1890. 



