NO. 8 ANATOMICAL LIFE OF THE MOSQUITO SNODGRASS 79 



are here fertilized by sperm discharged from the spermathecae. 

 Finally the eggs are passed out through the gonotreme at the time of 

 laying. 



The ovaries of the mosquito differ in several respects from the 

 usual structure of these organs in other insects. A typical insect 

 ovary consists of a group of slender tubes known as ovarioles opening 

 into the end of a lateral oviduct. The ovarioles taper upward and 

 end in filaments that unite in a common strand attached to tissues 

 in the neighborhood of the heart. A mature ovariole contains a series 

 of ripening egg cells of successively larger size, with the mature egg 

 in its lower end. Each egg is accompanied by a number of nutritive 

 cells, or so-called nurse cells, which are absorbed by the egg as it 

 matures. Each egg and its nurse cells are contained in a compartment 

 of the ovariole known as a follicle. The follicles appear as swellings 

 along the ovariole, increasing in size with the growth of the egg. 

 The egg cell and the nurse cells are formed by division of the undif- 

 ferentiated cells in a chamber, the germarium, in the upper end of 

 the follicle. The eggs do not pass down the ovarioles ; each ovariole 

 grows from the germarium as an egg leaves the lowermost follicle and 

 the latter disintegrates. 



In the mosquito ovary (fig. 30 B) the ovarioles (Ovl) are very 

 short and are arranged in rows along an axial cavity of the ovary. As 

 in other Diptera, each ovary is invested in a thin membranous sheath 

 (Sh) in which there are fine muscle fibers, and the sheath itself ends in 

 a terminal filament (tf) attached to tissues along the sides of the 

 heart. The muscle fibers of the ovarian sheath in Anopheles are said 

 by Nicholson (1921) to be striated, but Jones (1958) finds that those 

 of Aedes do not show a distinct striation in live, unstained whole 

 mounts at 1,000 magnification under phase optics. 



Each ovariole consists of a large egg-containing follicle with a small 

 projection on its free end representing the germarium and one or 

 two minute undeveloped follicles. The structure of the egg follicle of 

 Culex has been described by Nath (1924), and an account of the de- 

 velopment of the ovary and the development and nutrition of the eggs 

 in the ovary of Anopheles is given by Nicholson (1921), by Christo- 

 phers, Sinton, and Covell (1928), and by Mer (1936). The develop- 

 mental processes described in the mosquito differ little from those in 

 insects generally. 



Many female mosquitoes need a meal of blood for the production of 

 eggs. The eggs of Anopheles and Aedes are fully developed in two to 

 three days after the female has fed. It is said by Roy ( 1936) that in 



