Yue Chao, Hua Baozhen
Key Laboratory of Plant Protection Resources and Pest Management, Ministry of Education, Entomological Museum, Northwest A&F University, Yangling, Shaanxi 712100, China.
J Morphol. 2010 Nov;271(11):1366-73. doi: 10.1002/jmor.10879.
It is a long standing question whether the abdominal prolegs of holometabolous insect larvae are serially homologous with their thoracic legs. The histology and ultrastructure of proleg embryonic development in the scorpionfly Panorpa magna were studied using light and scanning electron microscopy. During the early embryonic development, paired primary abdominal appendages appeared laterally in line with the thoracic legs. Several hours later, a pair of proleg primordia arose along the midventral line on each of the first eight abdominal segments mesial to the primary abdominal appendages, which then ceased to grow and eventually degenerated into flat vestiges. Histological observation showed that the thoracic legs were obviously connected with lateral thoracic muscle cells, whereas the abdominal prolegs resembled secondary outgrowths. No apparent contact was observed between the lumen of abdominal prolegs and the hemocoel. After dorsal closure, each thoracic segment bore a pair of well-developed five-jointed legs, whereas the prolegs were unjointed, fleshy structure. The remnants of the primary abdominal appendages could still be clearly seen in the mature embryo. On the basis of the histological and morphological observation of the embryonic development, we confirm that the abdominal prolegs of Panorpidae lack the characters of the primary appendages; hence they are not serially homologous with the thoracic legs. The reasons why the primary abdominal legs are reduced in scorpionflies are briefly discussed.
全变态昆虫幼虫的腹足是否与其胸足具有系列同源性，这是一个长期存在的问题。利用光学显微镜和扫描电子显微镜研究了大蝎蛉（Panorpa magna）腹足胚胎发育的组织学和超微结构。在胚胎发育早期，成对的初级腹附肢在与胸足相对的侧面出现。几小时后，在前八个腹节中，每节的初级腹附肢内侧的腹中线上出现一对腹足原基，随后停止生长并最终退化为扁平的遗迹。组织学观察表明，胸足明显与胸部外侧的肌肉细胞相连，而腹足类似于次生突起。未观察到腹足管腔与血腔之间有明显的接触。背侧闭合后，每个胸节有一对发育良好的五节足，而腹足是无关节的肉质结构。在成熟胚胎中仍可清楚地看到初级腹附肢的残余部分。基于胚胎发育的组织学和形态学观察，我们证实蝎蛉科昆虫的腹足缺乏初级附肢的特征；因此，它们与胸足不具有系列同源性。文中简要讨论了蝎蛉初级腹足退化的原因。
