›› 1994, Vol. 37 ›› Issue (2): 171-177.

• RESEARCH PAPERS • Previous Articles     Next Articles

THE EMBRYONIC DEVELOPMENT OFSPHAERODEMA RUSTICUS

LI SHUN-ZHEN   

  • Online:1994-05-20 Published:1994-05-20

Abstract: A microscopic investigation on the embryonic development of Spherodema rustieus was conducted and the result indicates that the germ band occupies a large areaon the surface of the yolk in the egg and is polylobed in shape. It is divided into the cephalic, gnathal, thoracic and abdomenal lobes. In additionto anatrepsis, which caused the germ band partly immersing into the yolk, and katatrepsis, the germband from the head to the end of the abdomen had on arched movement just after anatrepsis, which resulted in the rising back of germ band to the dorsal surface of yolk and segmentation of the abdomen lobe. In the formation of the midgut, the post-rudiment was formed prior to the fore-rudiment, and they showed some difference in mode of extension, so that the midgut was differentiated into two parts morphologically-the tubular posterior portion and the elongated ovoid anterior portion.During the development of the nervous system, the ganglia tended to fuse and the abdominal ganglia finally fused into a compound ganglion and so did the thoracic ganglia. The relationship between the developmental stage of the embryo and the size of the egg was noticed and 'the function of the disintegrating dorsal organ discussed.

Key words: Sphaerodema rusticus——embryonic development——digestive system——nervous system——dorsal organ.