SLIME SLUGS, MYRIAPODS AND INSECTS 143 



shell or chorion. But a small hole, called micropyle, is left 

 at one pole in both these coverings, and through this a sper- 

 matozoan enters the egg while it is in the vagina, or a special 

 posterior part of it called the bursa copidatrix. 



The organs of the male that produce the spermatozoa are 

 called testes, and correspond in position and function to the 

 ovaries of the female. They are also composed of many 

 tubules, but they are closely pressed together to form a small 

 solid ovate mass. From each testis 

 runs a duct, the vas deferens, 

 through which the spermatozoa 

 pass to reach the single ejaculatory 

 duct, from which they are expelled 

 by the male at mating. 



TYPES or MOUTH-PARTS 



Corresponding to the great vari- 

 ety of food taken by insects is a 

 great variety in structure of mouth- 

 parts. The mouth-parts of the 

 honey-bee, which laps up flower 

 nectar, are very different from 

 those of the grasshopper, which 

 bites off and chews green leaves. 



And very different from either of mdlifica, reproductive organs, 

 .v ,1 ,1 sting and poison glands of 



these, again, are the mouth-parts que n> dors view 6 (Grea ti y 



of a butterfly or moth, or of a magnified; after Snodgrass.) 

 mosquito, or a squash-bug. 



To the economic entomologist a knowledge of the kind of 

 mouth-parts possessed by any insect pest is very important. 

 For on the structure of its mouth will depend largely the kind 

 of artificial remedy which must be devised to kill it. For ex- 

 ample, if an insect pest of fruit trees has a piercing and sucking 

 mouth, then spraying the surfaces of leaves with an arsenical 

 poison will do little good, for it gets its food, plant sap, from 

 the interior of the leaf or stem. But if it has a biting and chew- 

 ing mouth then such a poison sprayed over the leaves may be 



FIG. 59. Honey-bee, Apis 



