34 



ENTOMOLOGY. 



The external parts consist of the ovipositor (Fig. 1, B), 

 which is formed of two pairs of spines (rhabdites) adapted 

 for boring into the earth; and of the egg-guide (Fig. 4, eg), 

 a triangular flap guarding the under side of the opening of 

 the oviduct. 



The eggs are fertilized while in the oviduct during pair- 

 ing. The sperm-cells are secreted in little glands in the 



..-dr 



Fig. 29.— t, testis; v, vas 

 Fig. 28.— Male glands of a Bark -beetle, si, vas deferens; g, seminal vesicle 

 deferens; ho, testis; bl, sperm-sac; ag, ductus of Acheta campestris. — 

 ejaculatorius.— From Graber. From Gegenbaur. 



male called testes, which form a single mass of tubular 

 glands, resting in the upper side of the third, fourth, and 

 fifth segments of the hind body. Figs. 28 and 29 represent 

 these structures in other insects. 



The Egg.— In shape the eggs of insects are usually either 

 more or less spherical or oval. The shell which envelops 

 them is called the chorion. It is dense and brittle, and 

 often covered by a delicate mosaic-work of more or less 

 regular facets. In those of many moths the surface is finely 

 granulated, while in those of most butterflies the surface is 

 beautifully ornamented with ribs and furrows. 



In some eggs there are radiating appendages at one end, 

 as in those of Nepa (Fig. 30, 6), which surround the micro- 

 pyle; this being a microscopic opening through which a 

 spermatic particle enters to fertilize the egg. 



The mosquito lays its slender cylindrical eggs glued 

 together in a boat-shaped mass, which floats on the surface 

 of pools or cisterns; the Copris beetle, or " tumble-bug," 



