It may not be out of place to mention here a remarkable circumstance which not seldom attends a kind of water-scorpion (_Naucoris_ F.) occasionally to be met with in collections of Chinese insects. Its back is often covered with a group of rather large eggs, closely arranged; but whether these are its own eggs or those of some large species of water-mite (_Hydrachna_ Maïll.) has not been clearly ascertained. On the former supposition, the ovipositor must be remarkably long and flexile to enable the animal to place the eggs on its back. In confirmation of the latter it may be observed, that the species of the genus _Hydrachna_ usually attach their eggs to the body and legs of aquatic insects, as for instance _H. abstergens_ to the water-scorpion (_Nepa cinerea_), &c.[132]
2. After having thus laid before you some of the procedures of those insects that usually deposit their eggs in groups, either naked or defended by coverings of various kinds, I next proceed to a rapid survey of those of the species that commonly deposit them _singly_. Some of these, as for instance the Admiral Butterfly (_Vanessa Atalanta_), glue each egg carefully to its destined leaf by alighting on it for a moment. Another butterfly (_Hipparchia Hyperanthus_) whose caterpillar is polyphagous, drops hers at random on different plants. In general it may be observed, that all those larvæ which live in solitude, as in the interior of wood, leaves, fruits, grain, animals, &c., proceed from eggs laid singly by the female, which is usually provided with an appropriate instrument for depositing them in their proper situation. Thus the nut-weevil (_Balaninus Nucum_ Germ.) and also that of the acorn (_B. Glandium_) pierce a nut or an acorn with their long beak, and then deposit in the hole an egg, from which proceeds the maggot that destroys those fruits. Leeuwenhoek asserts that the common weevil (_Calandra granaria_) adopts the same process, boring a hole in every single grain of corn before it commits an egg to it, and at the same time, by this manoeuvre, prepares a small quantity of flour to serve for the food of the tender grub when it is first hatched[133]. It is probable that the Rhyncophorous or weevil tribe in general chiefly use their beaks for the purpose of depositing their eggs in different vegetable substances, and perhaps principally in fruit or grain. The tribe of gall-flies (_Cynips_) on the contrary, whose economy, detailed in a former letter[134], interested you so much, bore an opening for the egg with their spiral oviduct, which also conveys it.