Effects of stimulation on embryonic activity in the chick.

Effects of stimulation on the stereotyped and coordinated movements in the chick embryo were investigated using the type of stimulation (regular loud clicks) that is known to accelerate development and the time of hatching. The number of coordinated movements, the amount and approximate size of all activity, heart rates and, in 20-day embryos, respiration rates were assessed during a 15-min control period, a 15-min period of stimulation, and a 15-min period of no stimulation. The results showed an increase in the number of coordinated movements, but not their size, and some changes in the heart and respiration rates after the onset of stimulation. These effects occurred in most cases only after several minutes of delay. It is suggested that this delay may be connected with the reciprocal relationship between the coordinated movements and random motility in that the former may be triggered more readily at times when the latter are suppressed.