Embryonic Development Of Panorpa Emarginata Cheng (Mecoptera: Panorpidae)

Mecoptera, one of the most primitive orders in the Holometabola, are of great significance in the systematic study of insects. The embryology of Mecoptera shows the basic developmental pattern in holometabolous insects.The external morphology and embryogenesis of Panorpa emarginata were sudied by using scanning electro microscope and stereoscope.The whole embryonic development is divided into 10 stages, with the first-instar larva included, according to the major events happening during the development; The development of the external features of the embryos are described from stage 3 to the first-instar larva, and the outline of the embryonic development, from external observation, are given.The head is composed of an un-segmented acron at the anterirmost site and six following segments: the labral, antennal, intercalary, mandibular, maxillary and labial segments in succession. These different elements are separated by obvious inter-segmental sutures. The segmental status of the labral segment is found real, and the clypeolabrum, which develops from paired rudimental processes of the labral segment, is proved to be the appendages of the labral segment.The development of the 10th and 11th abdominal segment, the anal fork, the cercus and the dorsal processes are also carefully studied, clarifying the long-term suspicion about the structure and metamerism of mecopteran insects in terminal region of abdomen. The paired prolegs on 1st-8th abdominal segments develop from two middle processes that formed on the inner side of a pair of lateral processes, the true appendages of the abdomen which stop developing during their later development. Thus, the prolegs are not appendicular in origin.The origin of the ecdysial suture and dorsal closure line in the thorax and abdomen, as well as the germ type of P. emarginata are studied and discussed.The present study adds new data for insect Embryology, and also lays a foundation for the systematic analysis of Mecoptera, Insecta, or Arthropod from embryological standpoint and the study of evolutional and developmental mechanism in insects.