| Research Abstract |
The Protura, possessing many features shared together with myriapods, are one of the most primitive hexapod groups, so that this hexapod group is the most significant and interesting for elucidating hexapod origin, phylogeny in higher level and ground body plan. The comparative embryological approach is one of the most promising methods for such phylogenetical considerations. However, a minute size (av. 1 mm) of the hexapod makes its embryological study absolutely difficult, and our embryological knowledge on Protura remains to be utterly lacking. Moreover, we have little information even on the proturan ecology and life cycle, and we have been unable to even incubate proturans. For this reason, I planned the embryological study of Protura, and as the first step, I tried to elucidate the life cycle, to found a firm base for its embryological study.
Using an aceretomid proturan Baculentulus densus (Imadate, 1960) as materials, firstly, I identified the age of samplings and examined the seasonal change of female reproductive system. As a result, I succeeded in estimating the life cycle of the species : it has a life cycle of two years, and its reproductive season is late winter to early spring. Next, I tried to improve the incubation method of the proturans. After many trials, I gained a good result of incubation by using milled dead leaves as a substrate, and I succeeded in maintaining adults over months.
The frame work of the study concerned is outlined as "elucidation of hexapod phylogeny in higher level". Within its frame work, I also conducted embryological studies on apterygotes such as Archaeognatha, with special reference to the serial homology of gnathal appendages and the evolutionary transition of hexapod embryonic membranes. The results obtained were/are published as two original papers (in press) and two oral presentations.
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