. Elementary text-book of zoology. Zoology. 542 INSECTA. Dr some of the (J2 stride and of the Pujripara, are viviparous. As a rule, the eggs are laid shortly after fertilization, and before the commencement of the development of the embryo. In rare cases the embryo is already formed when the egg is laid. In the last case the segmentation and formation of the embryo take place in the vagina (fig. 451). The fertilization of the egg usually takes place during its passage through the oviduct, at the place where the receptaculum seminis opens. Since the eggs become invested with their resistant cJi
. Elementary text-book of zoology. Zoology. 542 INSECTA. Dr some of the (J2 stride and of the Pujripara, are viviparous. As a rule, the eggs are laid shortly after fertilization, and before the commencement of the development of the embryo. In rare cases the embryo is already formed when the egg is laid. In the last case the segmentation and formation of the embryo take place in the vagina (fig. 451). The fertilization of the egg usually takes place during its passage through the oviduct, at the place where the receptaculum seminis opens. Since the eggs become invested with their resistant cJiorion in the ovarian tubes, from the epithelial cells of which they originate for the most part during the larval life, it is necessary that there should be special arrangements which render possible the entry of the spermatozoa and the fertilization of the ovum. For this object there exist on the upper pole of the egg (the pole turned towards the egg-tubes during the passage of the egg) one or more pores known as micropyles,* which pierce the chorion and present a characteristic form and arrangement (tig. 452). The ova originate in the narrow terminal portion of the egg-tubes, which is often prolonged into a thin thread. Here the growth of the egg-tube takes place, as well as the differentiation of its contents into egg cells and ovarian epithelium. The ovarian tubes increase continuously in diameter towards the oviduct, in correspondence with the gradual increase of size undergone by the eggs, which are arranged one behind another in its lumen. Each egg occupies a chamber, and obtains an external resistant mem- brane (c/torioH,}, which is secreted by the epithelium which lines the chamber. The chorion shows in its external markings the pecu- liarities of the epithelium from which it was formed. Besides this type, which is found in Pulex and in many of the Neuroptera and Orthoptera, there is a second type of ovarian tube, distinguished from the first by a more complicated stru
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1884
