42 AN INTRODUCTION TO ENTOMOLOGY. 



alternate contraction and recovery of the figure of the abdomen in 

 two dimensions, viz., vertical and transverse. 



The Reproductive Organs. — In insects the male and female repro- 

 ductive organs are placed in different individuals. In many insects 

 there are marked external sexual differences of size, form, coloring, 

 or character of appendages. In others it is difficult to determine 

 the sex without dissection. The reproductive organs vary greatly in 

 form, but agree in certain general characteristics. They are con- 

 tained in the abdomen, are paired, and usually open by a common 

 duct near the caudal end of the body. (In the May-flies and Ear- 

 wigs the reproductive organs of each side have a distinct opening.) 



In the female there is in the abdominal cavity on each side an 

 ovary. This is a compound organ consisting of a series of parallel 

 tubes opening into a common oviduct. Sometimes these tubes are 

 attached to each other so as to form a compact body ; in other spe- 

 cies each tube is free for a greater or less part of its length. These 

 tubes are tapering in outline, the larger end being joined to the ovi- 

 duct. Within these tubes, even in the larval state, may be found 

 the developing eggs, each tube containing a single row of them grad- 

 ually increasing in size from the small end of the tube towards its 

 opening into the oviduct. The oviducts of the two sides unite a short 

 distance from the external opening and form the vagina. There are 

 usually accessory glands opening into the vagina, whose secretions 

 serve to surround the eggs or to fasten them to the objects upon 

 which they are laid. Connected also with the vagina are one or 

 more pouches, the receptdcula scminis, within which the reproduc- 

 tive fluid of the male is received and stored. This fluid retains its 

 fertilizing properties for a long time. Thus the queen-bee or ant 

 pairs but once, though she may continue to lay fertile eggs for years. 

 The fertilization of the eggs of insects takes place at the time they 

 are laid. There is in one end of the shell of the egg one or more 

 pores known as mlcropyles. Through these the spermatozoa enter 

 the egg, as it passes the opening of the receptacula seminis. 



In some cases, at least, it is not necessary that an egg should be 

 fertilized in order that the embryo should develop. This has been 

 proven with the Honey-bee. But so far as is known the unfertil- 

 ized eggs of the bee produce only males. 



The organs of the male consist of a number of tubular glands, 

 often coiled together so as to form an apparently compact body, 

 the testes. These like the ovaries are paired and located in the 

 abdominal cavity. The efferent ducts of these glands, the vdsa defe. 



