THE INTERNAL ANATOMY OF INSECTS 



157 



believe it to be the eleventh; embryological evidence supports the 

 latter view. 



In most insects there is a single external opening of the reproduc- 

 tive organs ; but in the Ephemerida and in a few other insects the two 

 efferent ducts open separately. 



Secondary sexual characters. In addition to differences in the 

 essential reproductive organs and in the genital appendages of the 

 two sexes, many insects exhibit what are termed secondary sexual 

 characters. Among the more striking of these are differences in size, 

 coloring, and in the form of certain organs. Female insects are 

 usually larger than the males of the same species; this is due to the 

 fact that the females carry the eggs ; but in those cases where the males 

 fight for their mates, as stag-beetles, the males are the larger. Strik- 

 ing differences in the color- 

 ing of the two sexes are 

 common, especially in the 

 Lepidoptera. In many 

 insects the antennae of the 

 male are more highly 

 specialized than those of 

 the female; and this is 

 true also of the eyes of 

 certain insects. These are 

 merely a few of the many 

 known secondary sexual 

 characters found in insects. 



Fig. 178- 

 Repro- 

 ductive 

 organs of 

 Japyx, 

 female 

 (After 

 Grassi) . 



Fig. 177. Diagram of thereproduc- 

 tive organs of a female insect; o, 

 ovary; od, oviduct; c, egg-calyx; v, 

 vagina; s,spermatheca; &c,bursa 

 copulatrix; sg, spermathecal 

 gland; eg, colleterial glands. 



there is a single ovarian tube 



b. THE REPRODUCTIVE 

 ORGANS OF THE 



FEMALE 



The general features of 

 the ovary. In the more 

 usual form of the ovaries 

 of insects, each ovary is 

 a compact, more or less spindle- 

 shaped body composed of many paral- 

 lel ovarian tubes (Fig. 177, o), which 

 open into a common efferent tube, 

 the oviduct. In Campodea, however, 

 and in certain other Thysanura the 



ovarian tubes have a metameric arrangement (Fig. 178). The num- 



