Some years ago these insects penetrated in the middle of the night through the open windows into one of the apartments of the military hospital at Louvain, and the next morning the skin of many of the patients, and especially the bed-linen, were covered with stains of blood. The physicians sent me some of these insects, not knowing whence they had come, nor whether they had been the cause of this annoyance. During the night, these Ornithomyæ had quitted their hosts to attack the soldiers. One of these insects, the banded Syrphus (_Syrphus balteatus_), when in the larva state, seizes the rose aphides, and sucks their blood with great eagerness. But it is not precisely a case of parasitism, when the wounds of soldiers are covered with larvæ, of which there were many sad instances in the Crimean war. There are flies which deposit their eggs in pus, as in all kinds of animal matter in a state of decomposition. 123 It is even said that these insects, deceived by the smell of the Arum flower, will lay their eggs on the pistil. The name of _Myasis_ has been given to the presence of these larvæ in a wound. Every one knows that bats are often literally covered with vermin. Among the many parasites which attack these little animals we find, besides the acaridæ, a _Pteroptus_ of great agility, which seems, as it were, to swim among the fur, and looks like a little spider or a microscopic crab. There are but few bats on which we do not find some of these, and we have sometimes seen them in such abundance, that it was impossible to touch a single hair without disturbing them. This species is usually called _Pteroptus vespertilionis_. It is constantly in motion, and glides among the fur like a mole in a sandy soil. Together with these Pteropti lives a parasite of gigantic size, which insinuates itself among the fur with equal dexterity, and bears the name of _Nycteribia_. This has long claws like a spider, and plunges deeply into the fur. These Nycteribiæ are found only on bats. They are often associated on these animals with fleas and mites. Mr. Westwood has written a monograph upon them. Mons. Plateau, our colleague, has quite recently described a new species in the "Bulletins de l'Académie de Belgique." Among the insects justly dreaded by man, and which follow him everywhere, is found one of the Hemiptera, known by every one under the name of bed-bug (_Cimex lectularia_). It is said that this insect was unknown in the capital of Great Britain before the fire of London in 1666. According to some entomologists, it was introduced 124 into Europe in some wood that came from America. It is only necessary to make this slight reference to the Cimices; their congeners are, for the most part, parasites of plants, and live on their sap. [Illustration: Fig. 16.--Bed-bug.]