Most of the species of cockroaches are black or brownish. Two among them, the _Blatta Germanica_ and the _Blatta Laponica_, which are to be met with in the woods round about Paris, have domesticated themselves in dwellings of the northern countries. They are a quarter of an inch in length. The Russians pretend that the former was imported from Prussia by their army, on its return from Germany, after the Seven Years' War (1756-1762). Till this period it was unknown at St. Petersburg, where now-a-days it is met with in great numbers. It lives in houses, and eats pretty nearly everything, but prefers white bread to flour and meat. The _Blatta Laponica_ devours the smoked fish prepared for the winter. The German naturalist, Hummel, made some interesting observations on the development and habits of the very prolific _Blatta Germanica_. It lays its eggs in a silky capsule, which is in the form of a bean, with two valves in the interior. This is drawn about for some time appended to the extremity of the abdomen, and after a time abandoned. Hummel placed under a bell-glass a female cockroach and a perfect egg-pouch, which had only just been abandoned by another female. He saw the cockroach approach the bag, feel it, and turn it about in all directions. She then took it between her front legs, and made a longitudinal opening in it. As the opening grew wider, little white larvæ were seen to come from it rolled up and attached together. The female presided at this operation. She assisted the larvæ to set themselves free, aiding them out gently with her antennæ. In a few seconds they were able to walk, when she ceased to trouble herself about them. The larvæ change their skin six times before reaching the perfect state. When they come out of their skin they are colourless, but the colour comes in a few minutes. At the fifth moult, which takes place three months after birth, they become pupæ, with rudimentary wings, the whole shape of the insect being well marked. The sixth, or last moult, takes place at the end of six weeks. The pupa is now changed into a perfect insect. The female is distinguished from the male by the greater size of her abdomen. [Illustration: Fig. 301.--The Cockroach (_Blatta orientalis_).]