ANATOMY AND PHYSIOLOGY 



'43 



In each ovarian tube, or ovariole, are found ova in succes- 

 sive stages of growth, the largest and oldest ovum being near- 

 est the oviduct. In the primitive type of egg-tube, as in Thys- 

 anura and Orthoptera (Fig. 183, A) every chamber contains 

 an ovum; in more specialized 

 types, every other chamber con- 

 tains a nutritive cell instead of a 

 germ cell, the nutritive cells serv- 

 ing as food for the adjacent ova 

 (B) ; or the nutritive cells, in- 

 stead 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 cells, 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. 

 184). In the male, the primary 

 germ cells form cells termed 

 spermatogonia; each of these 

 forms a spermatocyte, and this 

 gives rise to four spermatozoa. 



Hermaphroditism. The phenomenon of hermaphrodi- 

 tism, or the combination of male and female characters in the 

 same individual, occurs only as an extremely rare abnormality 

 among insects. Speyer estimated that in Lepidoptera only 

 one individual in thirty thousand is hermaphroditic. Bertkau 

 (1889) listed 335 hermaphroditic arthropods, of which 8 were 



Types of ovarian tubes. A, with- 

 out nutritive cells; B, with alternat- 

 ing nutritive and egg-cells; C, with 

 terminal nutritive chamber; c, ter- 

 minal chamber; e, egg-cell; ep, fol- 

 licle epithelium; f, terminal fila- 

 ment; s, strands connecting ova 

 with nutritive chamber; y, yolk, or 

 nutritive, cells. From Lang's Lelir- 

 bncli. 



