Abstract
In the inner walls of the thread pressing portion of the spinning tube of the silkworm, the dorsal chitinous plate, the ventral chitinous plate and the border chitinous plate are formed. All of these three types of chitinous plates are formed in the larvae of final instar. The border chitinous plate is never formed during other larval instars than the final one.
The spinning tube of a tetramolting larva on the first day of the third instar, which normally molts twice before the border chitinous plate is formed, was transplanted into the larva on the second day of the fourth instar. The growth of the host larva was normal and the transplanted spinning tube molted simultaneously when the host molted to the fifth instar. In the transplanted spinning tube, the border chitinous plate was formed as normal as in the spinning tube of the host larva.
It was found that the epidermal cells of the spinning tube, when forming the border chitinousplate, is controlled by the hormones that control growth of the larva.
