ABSTRACT
Two types of grafts from 3-day chick embryos were grown on the chorioallantoic membrane of a 9-day-old chick embryo: six isolated somites, 14−20; and six somites 14−20, with adjacent spinal cord. The activity of these noninnervated and innervated grafts was observed during their growth on the membrane.
No activity was observed at any time in the fifteen grafts of six somites grafted without spinal cord; but spontaneous twitching could be observed in twenty out of thirty-three grafts which contained sections of the spinal cord.
Histological examination confirmed that the twenty active transplants each contained a segment of spinal cord, and large nerve fibers could be traced to the muscle tissue in the grafts. The failure of the other thirteen grafts to show contraction is accounted for either by the absence of well differentiated muscles or by the absence of nerves invading them.
The muscle of the non-innervated, inactive pieces showed the same amount of differentiation as that of the innervated active grafts.
The activity observed in the innervated muscle tissue shows three different patterns : regular, with a periodicity similar to that of the intact embryo ; irregular and isolated twitches, i.e. less than six twitches in the 10-min. observation period.
It is concluded that the spontaneous motility of muscle developing on the chorioallantoic membrane is neurogenic and not myogenic. This finding supports the view that the spontaneous motility observed in vivo is neurogenic from its beginning.
