In special attempt to find the changes in the cuticular contributions to the water economy of silkworm during its development, some measurements and histological observations were made on the physico-chemical and microscopical properties of cuticle, its ether extractives, and epicuticular wax with the changes of the weight and surface of the body during the period extending from 4th larval instar to the pupation ecdysis. The results obtained are as follows:
1. There is a rapid loss in the weight of the body as well as its surface area during the prepupal period in contrast to a rapid increase in the 4th and 5th larval instars.
2. A large number of wrinkles appears all over the surface of the integument of the prepupa, especially profoundly on each intersegmental membrane. They increase in number and depth as the development proceeds. Histological observations show that these wrinkles are the invaginations of epi- and exocuticle into the part of endocuticle.
3. The cuticle increases in thickness during the 5th instar of the larva, more quickly in the prepupal period.
4. The amount of ether extractives ot the cuticle to the unit quantity of the cuticle as well as to the unit area of body surface increases from the 5th instar of the larva to after mounting of the larva.
5. The quantities of epicuticular wax, absolute, to the unit amount of the cuticle, and to the unit body surface do not change so markedly during the 5th larval instar, while they increase with the development of the prepupa to the conspicuous highest values just before pupal molting.
6. The melting points of the epicuticular wax are higher in the prepupal than in the larval period. They show a progressive elevation in the former, reaching the highest value in the late prepupa.
7. All the facts described above seem to tell a series of adaptations for the higher necessity for the restriction of water loss through the integument of the prepupa which do not take any amount of water from environment as compared to the larva to whom water is sufficiently supplied from mulberry leaves.
8. The same facts are also seen in the larva during the period of ecdysis during which the worm must be very sensitive to the transpiration.
9. It was proved that the exuviae from pupation ecdysis (=last larval ecdysis) consists mainly of the epicuticle. Consequently the wax obtained from the exuviae may be called the pure epicuticular wax.
10. The epicuticular wax from the pupal exuviae has almost the same physico-chemical properties as the one obtained by extraction from the living cuticle of the larva.
11. By abrading the living larva with fine alumina dusts or by weaping the integument with chloroform, we can prepare some amount of epicuticular wax, the properties of which are almost the same as the one obtained by extraction from the exuviae of the last larval instar or from the living cuticle.
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