VI 



,4 XTEXXA TA SEXUA L ORKA .VS 



489 



The thin terminal filaments of the egg tubes are generally attached to or near 

 to the dorsal vessel, and thus form a sort of suspender. The elements of these are 

 the same as those of the terminal chamber. The latter contains undifferentiated 

 cell elements as remains of the ovarial rudiments, from which proceed (either in 

 the embryo or the larva), on the one hand, the follicle epithelium of the ovarian 

 tubes, and on the other, the ripening eggs and nutritive cells contained in these 

 tubes. In the terminal chamber these 

 cell elements remain undifferentiated, 

 excepting when required for the renewal 

 of the follicle epithelium, eggs, and 

 nutritive cells in the adult insect. The 

 third section which leads into the oviduct 

 has usually the form of a string of beads. 

 It contains the ripening eggs. The 

 youngest and smallest lie nearest to the 

 terminal chamber, the oldest and largest 

 near the entrance into the oviduct. Two 

 sorts of egg tubes have been distin- 

 guished : those without nutritive cells 

 and those with nutritive cells. The 

 most simple are the ovarian tubes with- 

 out nutritive cells (Fig. 349, A], which 

 are found e.g. in the Orthoptera and 

 Apterygota (excluding Campodca). Here 

 in each tube there is a simple row of 

 eggs from the terminal chamber to the 

 oviduct. Between these consecutive eggs 

 the tube appears constricted, and this 

 causes the beaded appearance. Those 

 parts of the egg tube which lie between 

 two constrictions, each of which contains 

 one egg, are called ovarian chambers. 

 In the ovarian tube with nutritive cells 

 we must again distinguish two different 

 types. In the one type (Fig. 349, B) 

 there is a regular alternation of egg 

 chambers and nutritive chambers, each 

 of the latter containing one or more nutri- 

 tive cells, which serve for the nourishment 

 of the ripening egg contained in the 

 neighbouring chamber. The ovarian and 

 nutritive chambers may be distinctly separated externally by constrictions (Hymen- 

 optcra and many Colcoptera), or one nutritive and one egg chamber may lie in each 

 section of the ovarian tube, which is externally visible as a swelling (Lcpido-pd n\ 

 Di2)tcra). In the second type with nutritive cells, the actual tube consists (Fig. 349, 

 C) of ovarian chambers only, the nutritive cells here remain massed together in the 

 large terminal chamber. The single eggs in the tube are united with the terminal 

 chamber by connective strands, which convey the nutritive material to the eggs. 



Egg cells, nutritive cells, and the cells of the follicle epithelium (epithelium of 

 the chambers of the ovarian tubes) are, according to their origin, similar elements, 

 like the egg and yolk cells of the Platodes ; division of labour leads to their later 

 differentiation. Only a few of the numerous egg germs develop into eggs, the rest 

 serving as envelopes and food for these few. 



FIG. 349. Various types of ovarian tubes, 

 diagrammatic. A, Ovarian tube without nutri- 

 tive cells. B, Egg tube with alternating nutritive 

 and egg compartments. C, Ovarian tubes in 

 which the terminal chamber (ek) is developed 

 into a nutritive chamber, with which the develop- 

 ing eggs remain connected by means of strands 

 ('f.s) ; c/, terminal filament ; ck, terminal chamber ; 

 efa, egg compartments or chambers ; fe, follicle 

 epithelium ; df, yolk chambers. 



