1) Movements of spiracles were observed through a small elongate window which was made on the sieve plate cutting transversly a part of it and the rates of opening of spiracle at different environments were calculated. The observations were carried out in a room air-conditioned and in a quite weak current of air. The fifth instar female larvae reared in autumn were used as materials.
When the spiraculer valve was forced to close by some environment, there still remained a cavity unclosed. The rate of the remaining we called “a rate of opening at closed position”. And when it was forced to open, the rate of opening was called “a rate of opening at opened position”.
2) Generally there are some irregularities in the rates of opening at both positions, opened and closed. However, sometimes the rates at both positions are fixed at some and a definit point at the time when the moving membrane stops its movement.
3) The rate of opening in an individual varies with each spiracle and each spiracle shows peculiar reaction in such a case as the other spiracles were closed with a kind of Scotch tape. If the 1st thoracic spiracle is represented with thi and the 1st-8th abdominal spiracles with ab
1-ab
8 respectively, th
1 is usually most liable to close and its reaction to the closure of the other spiracles appears more gradually and duller than that of remaining spiracles. While ab
7 and ab
8 are most liable to open, and their reaction to the closure of the other spiracles comes gradually. Usually the rate of opening of ab
1-ab
6 are smaller than those of ab
7 and ab
8 and the younger the number of spiracles is, the more the spiracle is liable to open, and all of ab
1-ab
6 represent remarkable reaction especially to the closure of the observing spiracle out of ab
1-ab
6 with transparent Scotch tape for the convenience of observation. As for the degree of reaction to the closure of spiracles, in both the cases of the closure of cuticular surface and of the removal of sieve plates, if anterior abdominal spiracles are compared with posterior ones, the former is more sensitive than the latter.
4) Generally, the rate of opening of a spiracle increases when its relative spiracle of the segment is closed, and it more increases when only the observing spiracle is closed and it increases furthermore when both of the observing spiracle and its relative spiracle of the segment are closed.
5) When more than two spiracles belonging to successive two to three pairs of spiracles including the observing spiracles ab
3 or ab
7, are closed, the rate of the observing spiracles becomes larger to some extent in many cases. This phenomenon shows that the lack of O
2 and the excess of CO
2occurred within tracheae belonging to the closed spiracle excepting the observing spiracle and within tissues to which those tracheae are distributed, effect on other spiraclesthrough the tracheae.
6) The rate of opening of spiracles increases when the whole cuticular surface except spiracles is closed with vaseline. From this fact, it is supposed that silkworm is usually doing cutaneous. respiration to some extent.
7) The rate of opening of spiracles increased by the closure of cuticular surface recovers gradually after some lapse of time hours when silkworms are kept in a fast condition, and the recovery is quicker in ab
3 than in ab
8. The spiracles again tend towards opening if thereafter they feed on fresh mulberry leaves.
8) The rate of opening of spiracles at 24 hours after removal of the sieve plates is smaller than that at just after the removal. It is seemed that this fact owes to the function to prevent from metabolic unbalance caused by the removal of sieve plates.
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