158 



AN INTRODUCTION TO ENTOMOLOGY 



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ber of ovarian tubes differs greatly in different insects; in many 

 Lepidoptera there are only four in each ovary; in the honey bee> 

 about 150; and in some Termites, 3000 or more. 



The wall of an ovarian tube..— The ovarian tubes are lined with 

 an epithelial layer, which is supported by a basement membrane; out- 

 side of this there is a peritoneal envelope, composed of connective tis- 

 sue; and sometimes there are muscles in the peritoneal envelope. 

 The zones of an ovarian tube. — Three different sections or zones are 



recognized in an ovarian tube; first, 

 the terminal filament, which is the 

 slender portion which is farthest from 

 the oviduct (Fig. 179, t); second, the 

 germarium, this is a comparatively short 

 chamber, between the other two zones 

 (Fig. 179, g); and third, the vitellarium, 

 which constitutes the greater portion of 

 the ovarian tube. 



The contents of an ovarian tube. — In 

 the germarium are found the primordial 

 germ-cells from which the eggs are devel- 

 oped; and in the vitellarium are found 

 the developing eggs. In addition to the 

 cells that develop into eggs there are 

 found, in the ovarian tubes of many 

 insects, cells whose function is to furnish 

 nutriment to the developing eggs; these 

 are termed nurse-cells. 



Depending upon the presence or ab- 

 sence of nurse-cells and on the location of 

 the nurse-cells when present, three types 

 of ovarian tubes are recognized: first, 

 those without distinct nurse-cells (Fig. 

 179, A) ; second, those in which the eggs 

 and masses of nurse-cells alternate in the 

 ovarian tube (Fig. 179, B); and third, 

 those in which the nurse-cells are 

 restricted to the germarium (Fig. 1 79, C), which thus becomes a nutri- 

 tive chamber. In the latter type the developing eggs are each con- 

 nected by a thread with the nutritive chamber. 



The egg-follicles. — The epithelium lining of the ovarian tube 

 becomes invaginated between the eggs in such a way that each egg is 



fa: 



ABC 



Fig. 179. — Three types of 

 ovarian tubes; e, e, e, 

 eggs; n, n, n, nurse-cells 

 (After Berlese). 



