Class insecta 527 



duced. The ovarioles unite at their bases to form the oviduct. The 

 oviducts from each side join to form the median vagina. At the base 

 of the ovary, the oviduct has a pocketHke enlargement, the egg pouch. 

 Opening into the vagina are paired accessory glands and a median 

 unpaired seminal receptacle. The sperm received during copulation are 

 stored in the seminal receptacle. The vagina opens at the ovipositor 

 near the ventral egg guide. This latter is a structure which guides the 

 eggs during their passage through the ovipositor. 



Fertilization is internal, and usually occurs during late summer 

 or early fall. As the eggs are produced in the ovary, they are sur- 

 rounded by a thin vitelline membrane and a heavy shell, the chorion. 

 The chorion contains a micropyle through which the sperm enters for 

 fertilization. The female deposits the eggs in the ground by using her 

 ovipositor to construct a small tunnel. Masses of eggs are fastened 

 together by a sticky secretion. 



Immediately after being laid, development starts in the eggs. 

 After about three weeks when the embryo is formed, the diapause 

 occurs. During this time, further development stops, enabling the 

 embryo to overwinter in safety. In the spring, development is resumed 

 and the young hatch and come to the surface. Several molts follow 

 before the adult form is attained. 



STRUCTURAL VARIATIONS 



Inasmuch as insects live in so many and such varied habitats, it 

 is to be expected that they will show a great variety of structural adap- 

 tations to meet the varying environmental requirements. These vari- 

 ous modifications may be seen in both the external and internal struc- 

 tures, but are most evident in the mouth parts and in the appendages. 



The Mouth Parts. — While the mouth parts of the grasshopper 

 are very generalized in their structure, other insects show amazing 

 modifications of this basic type. The three main elements of the in- 

 sect's mouth parts are the mandibles, maxillae, and labium. Also 

 closely associated with the mouth parts is the hypopharynx which is 

 an unsegmented outgrowth of the body wall and usually forms a pro- 

 truding tube. These parts are variously modified in the different in- 

 sects, depending upon the food habits. Fundamentally these parts are 

 derived from a type of biramous appendage similar to the swimmeret 

 of the crayfish. 



