FOUR PI"I(iL1RES
A number of investigations have previously been made on the development of the enzyme choliiiesterase in Aniblystoma punctatum embryos (Youngstrom, '38 ; Sawyer, '43a, b ; Boell, '48). In these studies, cholinesterase determinations were made on extracts or hoixiogenates of whole embryos, and the results are in agreement in showing that enzyme activity increases sigiiificaiitly at the time when the embryo is first capable of responding to tactile stimulation by making rapid, repetitive movements. Sawyer ( '43) concludes from his observationq that functional niaturation of the neuromiiscnlar apparatus is associated with an increase in cholinesterase content of the embryo and that the development of this enzyme is a good biochemical criterion of the attainment of functional capacity.
I t is apparent from the classical work of Coghill ( '29) that the various regions of the central nervous system do not become functionally matiire simultaneously. Instead, Coghill's work shows, as do the more recent studies of Detwilcr ( '48), that functional differentiation of the nervous system, at least in so far as control of motor activity is concerned, begins in the spinal cord. Maturation then proceeds in a caudad to cephalad direction, with the mesencephalon assuming dominance over Supported in part by a grant from The Amerieaii Caneer Sneiety through the NRC Gomrriitee 011 Growth.