There are other kinds of lice, but we will only mention the louse which infests beggars and people of unclean habits, _Pediculus humanus corporis_, producing the complaint called phthiriasis. In the victims of this disease these parasites increase with fearful rapidity. This dreadful disorder is often mentioned by the ancients. King Antiochus, the philosopher Pherecydes of Scyros, the contemporary and friend of Thales, the dictator Sylla, Agrippa, and Valerius Maximus, are said to have been attacked by phthiriasis, and even to have died of it. Amatus Lusitanus, a Portuguese doctor of the sixteenth century, relates that lice increased so quickly and to such an extent on a rich nobleman attacked with phthiriasis, that the whole duty of two of his servants consisted in carrying away, and throwing into the sea, whole basketfuls of the vermin, which were continually escaping from the person of their noble master. Little is known at the present day of the details of this complaint, though it is observed frequently enough in some parts of the south of Europe, where the dirty and miserable inhabitants are a prey to poverty and uncleanliness--two misfortunes which often go together. In Gallicia, in Poland, in the Asturias, and in Spain, we may find many victims of phthiriasis. Lice increase with such rapidity on persons thus attacked, that it is common to attribute their appearance to spontaneous generation alone. But the prodigious rapidity of reproduction in these insects sufficiently explains their increase, especially when it is admitted that it is possible for the female louse to reproduce young without the agency of the male. The Thysanura or "Skip Tail" tribe are small insects, which are better known on account of the beauty of their microscopic body scales than for any interesting habits or instincts. They do not undergo metamorphosis. The Fish Scale or _Lepisma saccharina_, and the Skip Tail or _Podura plumbea_ belong to the Thysanura. II. DIPTERA. All suctorial insects which in the perfect state possess only two membranous wings, are called Diptera, from two Greek words--[Greek: dis], twice, and [Greek: pteron], wing. The Diptera were known and scientifically described at a very early date. They are frequently mentioned by Aristotle in his "History of Animals;" and he applied the term to the same insects as now constitute the order. The absence of the second wings, common to other insects, which are in this case replaced by two appendages, which have received the name of balancers,[10] because they serve to regulate the action of flight, constitutes the chief characteristic of the Diptera. Let us, however, give a glance at their other organs, which have more or less affinity with those which exist in other classes of insects, preserving, nevertheless, their own especial characteristics. [10] Sometimes called _halteres_.--ED.