Abstract
1) Mitotic frequency was estimated in the presumptive skeletal mesoderm of the hindlimb bud in toad larvae at limb bud stages, i.e. , at stages 3-5. 2) When the larva was reared at an optimal temperature of. 20±1 ℃, mitotic frequency was extremely high at stage 4. Thus, this stage seemed to be most sensitive to teratogenic agents. 3) In the larva reared at a high temperature of 30±1 ℃, not only mitotic frequency was lower than that in the larva reaed at 20±1 ℃, but also no increase of mitotic frequency was recognized at stage 4. 4) The cause of defective digital malformations produced by a high temperature of 30±1 ℃ was discussed in relation to decrease of mitotic frequency in the presumptive skeletal mesoderm.
