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ANATOMY AND PHYSIOLOGY 



125 



183) arise in the testicular follicles from a germinal 



consist, as in vertebrates, of a head, middle- piece and a vibratile tail 

 without entering into the finer structure. 



Female Organs. Each ovavy (Fig. 184) consists of one or more 

 tubes opening into an oviduct. The two oviducts enter a common duct, 

 the vagina, which opens to the exterior, often through an ovipositor. 

 Frequently the vagina is expanded as a pouch, 

 or burs a copulatrix, though in Lepidoptera 

 the bursa and the vagina are distinct from 

 eacrTother and open separately (Fig. 185). 

 In most insects a dorsal evagination of the 

 vagina forms a seminal receptacle, or sperma- 

 theca, from which spermatozoa emerge to 

 fertilize the eggs. The accessory glands, 

 either paired or single, provide a secretion for 

 attaching the eggs to foreign objects, cement- 

 ing the eggs together, forming an egg-capsule, 

 etc. 



In each ovarian tube, or ovariole, are found 

 ova in successive stages of growth, the largest 

 and oldest ovum being nearest the oviduct. 

 In the primitive type of egg-tube, as in Thy- 

 sanura and Orthoptera (Fig. 186, A) every 

 chamber contains an ovum; in more special- 

 ized types, every other chamber contains a 

 nutritive cell instead of a germ cell, the nutri- 

 tive cells serving as food for the adjacent ova (B) ; or the nutritive cells, 

 instead of alternating with the ova, may be collected in a special 

 chamber, beyond the ovarian chambers (C). An egg- tube is usually 

 prolonged distally as a terminal filament or suspensor, the free end of 

 which is attached near the dorsal vessel. 



Ovaries and testes arise from indifferent cell or primitive germ cells, 

 which are at first exactly alike in the two sexes. In the female, certain 

 of these cells form ova and others form a follicle around each ovum (Fig. 

 187). In the male, the primary germ cells form cells termed spermato- 

 ^omaj each of these forms a spermatocyte, and this gives rise to four 

 spermatozoa. 



Hermaphroditism. The phenomenon of hermaphroditism, defined 

 as " the union, real or apparent, of the two sexes in the same individual," 

 occurs among insects only as an extremely rare abnormality (except in 



PIG. 183. Spermatozoa. 

 A, grasshopper; B, cockroach, 

 Blatta; C, beetle, Copris. Af- 

 ter BUTSCHLI and BALLOWITZ. 



