1. An English anautogenous race and three European strains of the autogenous race of Culex pipiens have been studied comparatively for 3 years under laboratory conditions.2. Prolonged illumination has an activating influence on females of the anautogenous race, both hibernating and laboratory bred, and greatly stimulates gorging.3. With the aid of artificial light during the winter months the anautogenous race has been kept breeding in the laboratory throughout the year for eleven generations without the occurrence of cyclical hibernation (asthenobiosis). Consequently it is suggested that the length of daylight may be a factor of importance in controlling the natural hibernation of females of this race.4. Females of the English anautogenous race, whether of hibernating, or of active generations, laid normally after one blood meal and did not exhibit gonotrophic dissociation. They also oviposited readily after being artificially fed on bird blood.5. Unfed females lived for a maximum of 19 days and never accumulated fat-body autotrophically.6. Females, if fed on apple for 5 weeks, accumulated sufficient reserves to enable a small percentage of them to survive 15 weeks of starvation.7. In the anautogenous race pairing always begins in the air although it may be completed on the ground. The females do not lay without a blood meal, and they show little tendency to bite man but bite birds voraciously.8. Strains of the autogenous race of C. pipiens were obtained from rural areas in Greece, Malta and Hungary and have been maintained in the laboratory for over 3 years.9. Continuous breeding under autogenous conditions (no blood meals) for several years and through forty-five to forty-nine generations has had no deleterious eflect on these autogenous strains.10. Spanogyny, or the gradual decrease in the numbers of females produced in succeeding generations, does not necessarily follow prolonged autogeny if the cultures are kept under favourable conditions.11. Males of the autogenous race pair with resting females, so that pairing can take place in very small areas.12. Cross-mating was easily obtained between the two races, autogenous and anautogenous, in both directions: male autogenous + female anautogenous; and male anautogenous + female autogenous. Stenogamy and autogeny are hereditary characters. Stenogarny always appears in the F1 generation, but autogeny sometimes appears in the F1 generation and sometimes not until the F2 generation.13. Eggs are quickly killed by temperatures below freezing-point; and young larvae die within 24 hours at 0° C. Adults, even hibernating females, die within 4 days at −16° C.

1. Anautogenous English and autogenous Greek, Hungarian, Maltese and cross-bred strains of C. pipiens were infected with an Algerian and a German strain of P. relictum.2. The different strains of C. pipiens behaved similarly as regards susceptibility and transmission towards the same strain of P. relictum.3. The two strains of malaria differ in the infection rate produced in mosquitoes. The Algerian strain produces an infection rate of about 89 per cent., while that of the German strain is only about 43 per cent.4. The difference in the infection rates of the two strains is not due merely to differences in the number of gametocytes formed.5. In general C. pipiens fed on birds infected with the Algerian strain of malaria became more heavily infected than those fed on birds infected with the German strain.6. C. pipiens were infected in some cases by feeding on birds with chronic infections of the Algerian strain of P. relictum, but not when fed on birds with chronic infections of the German strain.7. No seasonal influence was found as regards the infection of C. pipiens by P. relictum.8. The Algerian strain of malaria was successfully transmitted by English, Greek, Hungarian, Maltese and Greek-Hungarian strains of C. pipiens, and the German strain of malaria by English, Greek, Maltese and Greek-English strains of C. pipiens.

1. Perispiracular glands are present in the larvae of Anopheles and Culex.2. These glands secrete an oily substance which is responsible for the hydrofuge properties of the spiracular region of mosquito larvae.3. The differential wetting of the spiracular region and the action of oil on mosquito larvae depend on the presence of this oily secretion.