[Development of prospective diapause-germs (Bombyx mori L.)in vitro without dormancy : I. Extracts of diapause or nondiapause eggs in defined stages with or without a yolk depot].

1. Naked germ-anlagen and germ-bands during segmentation from univoltine strains ofBombyx mori L. were used without HCl-treatment for culturein vitro. With improved methods germs could develop without their prospective diapause until they had finished organogenesis and if kept in hanging drops nearly one month. 5 culture mediums contained defined extracts: (1) eggs with prospective diapause germs, (2) eggs with nondiapausing germs (3) eggs with germbands in eudiapause, (4) eggs with embryos after diapause and (5) eggs with nondiapausing embryos. In every case explanted germs developed at least to fully segmented germbands (stage of dormancyin ovo) but often further. 2. In culture medium (1), (2), (4), (5) 64-73% of germ-anlagen develop to embryos with articulate limbs and open backs, but in medium (3) only 55%. On the contrary germbands develop to this stage and to shortened embryos in medium (1) only to 38%, in (2) to 5%, in (3) to 12% but in (4) to 75% and in (5) even to 84%. In culture medium (3) there occur abnormal differentiations. 3. A store of yolk or of yolk and serosa separately from the tested germ allows development in many more cases without dormancy and to small larvae with closed backs, with eye pigmentation and muscle contractions. Embryos with appendage formation grow to 100% in culture medium (4) with depositum. Therefore it is the most efficient medium for experiments with fragmented parts of a germ. 4. The different rate of development without dormancy with germbands in culture medium (1) to (5) points to their competence for determining factors of diapause. One day diapausing germbands inovo arein vitro with yolk stores able to develop further. But 2 days old germs in dormancy also with stores cannot any further develop. The germband is definitively determined to eudiapause. 5. Also the material in the stores can develop. Yolkcells may aggregate and will be enclosed by the serosa. Together they form bubbles which pulsate and yolk inside. This material could include factors for diapause, but also for basal metabolism and for syntheses of cell differentiation. Possibly it couldclean also the drop. 6. The results invite discussions aboutin vitro methods, about the ability of the explanted germ for formation and about factors determining dormancy or organogenesis. The selected hypothesis requires experiments with a medium without egg-extract but with stores from extraembryonal egg-materials and it needs investigations of regulation in cell differentiation.