The different types of larvæ represented in figure 81 were formerly supposed to belong to different species but Blanchard regards them as merely various stages of the same species. It is only very recently that the early stage and the method by which man becomes infested were made known. [Illustration: 83. Dermatobia cyaniventris (×1¾). After Manson.] [Illustration: 84. Mosquito carrying eggs of Dermatobia cyaniventris. After Surcouf.] About 1900, Blanchard observed the presence of packets of large-sized eggs under the abdomen of certain mosquitoes from Central America; and in 1910, Dr. Moralès, of Costa Rica, declared that the Dermatobia deposited its eggs directly under the abdomen of the mosquito and that they were thus carried to vertebrates. Dr. Nunez Tovar observed the mosquito carriers of the eggs and placing larvæ from this source on animals, produced typical tumors and reared the adult flies. It remained for Surcouf (1913) to work out the full details. He found that the Dermatobia deposits its eggs in packets covered by a very viscid substance, on leaves. These become attached to mosquitoes of the species _Janthinosoma lutzi_ (fig. 84) which walk over the leaves. The eggs which adhere to the abdomen, remain attached and are thus transported. The embryo develops, but the young larva (fig. 82) remains in the egg until it has opportunity to drop upon a vertebrate fed upon by the mosquito. Muscidæ The following MUSCIDÆ, characterized elsewhere, deserve special mention under our present grouping of parasitic species. Other important species will be considered as facultative parasites. _Stomoxys calcitrans_, the stable-fly, or the biting house-fly, is often confused with _Musca domestica_ and therefore is discussed especially in our consideration of the latter species as an accidental carrier of disease. Its possible relation to the spread of infantile paralysis is also considered later. The _tsetse flies_, belonging to the genus _Glossina_, are African species of blood-sucking Muscidæ which have attracted much attention because of their rôle in transmitting various trypanosome diseases of man and animals. They are characterized in Chapter XII and are also discussed in connection with the diseases which they convey. _Chrysomyia macellaria_, (= _Compsomyia_), the "screw worm"-fly is one of the most important species of flies directly affecting man, in North America. It is not normally parasitic, however, and hence will be considered with other facultative parasites in Chapter IV. [Illustration: 85. Larva of Auchmeromyia luteola. After Graham-Smith.] [Illustration: 86. Auchmeromyia luteola (×4). After Graham-Smith.]