13, od) leads, and in some of the more primitive insects (bristle-tails, earwigs, may-flies) the two oviducts open separately direct to the exterior.
In insects so widely separated as bristle-tails and moths this occurs occasionally.
These two endoderm-rudiments embryonic membrane formed by delamination from the blastoderm, ultimately grow together and give rise to the epithelium of the midwhile in a few insects, including the wingless spring-tails, the emgut.
Wingless insects, such as spring-tails and lice, make their appearance in the form of miniature adults.
Consequently the modern order Aptera comprises only a very small proportion of Linnaeus's " Aptera " - the spring-tails and bristle-tails, wingless Hexapoda that stand evidently at a lower grade of development than the bulk of the class.