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Siberians have given the name "gnus" to the blood-sucking dipterous insects which attack man and domestic animals. During the summer in many regions of Siberia and the Far East, especially in forest and marshy areas, many thousands of winged blood-sucking insects attack man, pierce his skin with their needle-like mouth parts and annoy him with their bites. Even if one insect is driven away, one hundred or one thousand more replace it. At no time during a summer day can man be free of this pest. Domestic and wild animals are also annoyed and attacked by these insects.These dipterans affect human health and animal behavior. Productivity at work sites also suffers due to these insects. The full impact of these pests has not been adequately studied but available data indicate significant reduction in output of labor exposed to annoying blood-sucking mosquitoes. According to the data collected by Maslov and Shamrai (1955), labor productivity of the Eleventh Forestcutting Brigade in the Vyazemsk district of Khabarovsk region averaged 88% in the summer of 1953, when there was no protection from blood-sucking mosquitoes. Productivity rose to 110% in the same brigade when dimethylphthalate was used as a repellent. Similar data are available for the Arkhangelsk region (Kalmykov, 1955) and the Karelian Autonomous Soviet Socialist Republic (Lutta, 1956). 8 partly reduced. Having studied this aspect in some members of the family Culicidae, Marshall, Staley and Staley (1935) presented some interesting data on the comparative measurements of the length of maxillae and mandibles in percentage of the length of the proboscis: according to their data, in Culiseta mosquitoes, the maxillae of males are marked by maximum relative length compared to other Culicinae. The results of a special study of this character in various members of Culisetina are presented in Table 1. The table shows that the mandibular index (ratio of its length to that of proboscis along with labial palps) is greatest in males and most variable in members of the subgenus Culiseta s. str. and in Allotheobaldia longiareolata. This index is noticeably low in members of the subgenus Culicella. The maxillary indices also vary in roughly the same proportion (Table 1).Attention should be paid to the structures of the maxillary palps 11 16 pal segments as in other Culicidae (Ivanova, 1960) but only tactile sensillae (trichogen cells) are present on the terminal segment. Maxillary palps of females are also 5-segmented, but the first two are fairly completely fused, the 3rd and 4th segments normal (4th is the longest), while the 5th is underdeveloped and is found as a small knob or button, often hidden in the pit of the 4th segment. In some species, the 5th segment may even be double in length, as pointed out by Natvig (1948) for Culiseta annulata and as mentioned in our data for C. annulata annulata and sometimes for C. bergrothi and alaskaensis. The length of the palp averages 16-29% of that of the proboscis, with a range from 10 (in C. alaskaensis, C. glaphyroptera an...

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Sporoblast and sporozoite formation from oocysts of the avian malarial parasite, Plasmodium gallinaceum, after the seventh day of infection in Aedes aegypti mosquitoes offers an interesting example of differentiation involving the appearance and modification of several cellular components. Sporoblast formation is preceded by (a) invaginations of the oocyst capsule into the oocyst cytoplasm, (b) subcapsular vacuolization and cleft formation, (c) the appearance of small tufts of capsule material on the previously noted invaginations, and (d) linear dense areas located just below the oocyst plasma membrane which predetermine the site of emerging sporozoites from the sporoblast. The subcapsular clefts subdivide the once-solid oocyst into sporoblast peninsula. Within the sporoblast, nuclei migrate from the random distribution seen in the solid oocyst and come to lie at the periphery of the sporoblast just below the linear dense areas noted in the earlier stage. A typical nuclear fiber apparatus occurs in most of the nuclei seen in random sections at this stage although such a fiber apparatus may occasionally be seen in the solid oocyst stage. The nucleus, its associated fiber apparatus, and the overlying dense area appear to induce the onset of sporozoite budding from the sporoblast as well as the formation of the sporozoite pellicular complex and the paired organelle precursor. Several mitochondria are present in each sporozoite, in contrast to the single mitochondrion seen in the merozoites of the erythrocytic and exoerythrocytic stages of avian malaria infection. The paired organelles and associated dense inclusion bodies are formed by condensation of an irregular meshwork of membranebound, coarse, dense material. The nature of small, particulate cytoplasmic inclusions is described.

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