Deprived of their brains immediately after pupation, Bombyx pupae sometimes do not become imaginal surviving more than a hundred days at 25°C. Such pupae are called in terms of “Dauer-pupae” (KOBAYASHI 1955, 1957). That the rates of occurrence of the dauer-pupae vary with the varieties and also with the rearing seasons even though the operations were made at the same period, i. e., immediately after pupation, was studied.
On the difference among varieties: As shown in Table 1, in two varieties, C115 and F₁ hybrid N122×C115, a considerable number of the dauer-pupae were obtained. While no dauerpupa was obtained in the variety N122.
On the difference among those in different seasons: They were obtained more in spring than in summer and in late autumn as shown also in Table 1.
From the results mentioned above, it has become clear that the critical point of the brain hormone concerned in the imaginal differentiation through affecting the prothoracic gland differs according to the varieties and to the rearing seasons.
What is the most important factor or factors that cause the seasonal differences in the rearing conditions? To answer the question, the measurements have been made on the rearing temperature and the feeding duration of each instar in parallel with the experiment (Table 2). Under definite conditions of the other environmental factors, the duration of each instar must be shortened with increasing temperature. As shown in Tables 1 and 2, however, the durations in summer and in autumn were not so shortened comparing with those in spring as expected from the temperature differences. The relative humidity was controlled approximately in optimum. Therefore, so far as this experiment is concerned, it is unlikely that the temperature as well as the humidity are essentially important factors on the seasonal differences in the duration.
On the other hand, the quality of the mulberry leaves used in the experiment was tested biologically using the unstable trimoulter strain, Dm³/+m³, in which tetramoulters should occur mixing with trimoulters in the same batch in proportion to the deterioration of quality of mulberry leaves they fed on. As shown in table 3, far less tetramoulters occurred in spring than in summer and in late autumn. This fact shows that the leaf quality during the earlier larval instar in spring has been superior to those in summer and autumn.
Thus, it is highly probable that the seasonal differences in a rate of appearance of the dauer-pupae depends upon the leaf quality. It may be concluded that the effective threshold of the brain hormone differs among the varieties and is varied with nutritional condition; a favorable one results in later attaining to the threshold.

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Respiratory enzyme activities in the homogenate and the mitochondria of the mid-gut of Bombyx larva were measured both with cytoplasmic polyhedrosis-diseased and with healthy worms.
The results obtained were as follows:
1. Inhibition rate of endogenous respiration of the diseased homogenate by 0.01M EDTA is less than that of the healthy one.
2. Both in the healthy and the diseased worms, the EDTA inhibition was recovered by adding such metals as Mg⁺⁺, Mn⁺⁺, Co⁺⁺ and Fe⁺⁺⁺ with the exception of Cu⁺⁺. The rates of the recovery differ between the healthy and the diseased ones; in the former the recovery does not reach the level of normal endogenous respiration; but in the latter it is remarkable.
3. Both activities of cytochrome oxidase and succinic dehydrogenase in the mitochondria did not show any difference between the healthy and the diseased worms.
4. Oxidation of succinate, malate and glutamate by both the homogenate and mitochondria of the diseased worm were lower than those in the healthy ones.
5. Activation by adding DPN on the glutamate oxidation in the mitochondria of the diseased was less than that in the healthy.
The same relation was found in the case of activation by adding ATP on the succinate oxidation.

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In the routine method of artificial hatching of silkworm eggs, eggs 20 hours after laying are immersed in hydrochloric acid (specific gravity is 1.075) for about 5 minutes at 46°C.
In this paper two experiments on the artificial hatching by using hydrochloric acid at low temperature (-5°C or 5°C) are reported.
In the first experiment, eggs of Nichi 122, Nichi 124, Shi 122 and Shi 124 (all of them laid in July) were used as materials, and in the second experiment, eggs of (Nichi 122×Nichi 124)×(Shi 115×Shi 124).
Artificial hatching treatment was applied to the eggs 18 hours after laying, and after the treatment, the eggs were incubated at 25°C. The results obtained were as follows.
1. First experiment. By immersing the eggs in the hydrochloric acid (specific gravity, 1.100) for 12 hours at 5°C, more than 90% of them hatched. But when the time of immersing was so long as 24 or 36 hours, the percentage of hatching decreased, and in the case of 36 hours, the percentage of hatching was so low as 60-71%.
2. Second experiment. Eggs were immersed in the hydrochloric acid (specific gravity, 1.100 or 1.130) at -5°C or 5°C, and good results were obtained in the following cases. In the case of specific gravity of hydrochloric acid being 1.100, the time of immersing being 75 hours, and the temperature being -5°C, the percentage of hatching was 90.3%; in the case of the same specific gravity, but a time of immersing of 15 hours and a temperature of 5°C, the percentage of hatching was 93.4%; in the case of specific gravity being 1.130, a time of immersing of 4-10 hours, and a temperature of -5°C, the percentage of hatching was between 94.4% and 96.4%; in the case of the same specific gravity, and an immersion period of 3-4 hours, and a temperature of 5°C, the percentage of hatching was between 96.0 and 97.5%.

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Some crystalline substances are formed in the nuclei of some cylindrical cells in the mid-gut of the cytoplasmic polyhedral-diseased silkworms.
The histological and cytological investigations have been carried out concerning the formation and stainability of these crystalline substances. The results obtained are as follows:
1. The crystalline substances are usually square in form, but some are round or polygonal, and are 6-10 micron in diameter.
2. The crystalline substances are acidophil, and particularly, can be stained well with orang G, eosin, phloxin or bromophenol blue after they are hydrolyzed in 1N HCl at 60°C for several minutes. However, they can not be stained with pironin, haematoxylin or through Feulgen reaction.
3. It is most probable that the formation of these crystalline substances may have some relation with the nucleolus, and that the nuclei of the infected cylindrical cells continue to produce the nuclear substances which lead to the formation of these crystalline substances even in the process of the polyhedral formation in the cytoplasm, and that some of these nuclear substances are crystallized in the nucleus, keeping a close relation with the nucleolus.

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Effects of the temperature (25°, 35° and 45°C) of washing water to produce loose-formed eggs on the unseasonal hatching of them have been investigated during 90 days after laying, using hibernating-eggs of C122 and Nikko.
1) Difference in temperature of washing water has no significant effects on the unseasonal hatching of eggs.
2) It was calculated by the equation of regression curve that the optimum temperature of washing water, at which the unseasonal hatching of eggs was most poor, was about 30°C.
3) It was shown that the unseasonal hatching of eggs had tendency to outbreak frequently in the period from the day of laying to the 3rd day after laying and from the 40th to 90th day and outbroke most frequently on the next day of laying, using the water of 25°, 35° and 45°C.

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[in Japanese]

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[in Japanese]

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