[A histochemical study of cholinesterase in the axial mesoderm ofTriturus cristatus]

1. InTriturus cristatus embryos (Harrison stages 15-42) the development of cholinesterase (ChE) activity in the axial mesoderm was investigated. 2. After embedding in polyethylene glycol the histochemical technique of Karnovsky and Roots (preincubation in maleinimid to block sulfhydryl groups) and that of Koelle were employed on serial sections. 3. In early neurula stage ChE is found in the presumptive notochordal and somite material of the archenteron roof. 4. The notochord is ChE-positive from late neurula stage until Harrison stage 25. Then the cells loose their activity in cranio-caudal progression. 5. The subnotochordal rod is ChE-positive from Harrison stage 21/22 until Harrison stage 30-33. 6. The somites are ChE-positive as they develop. 7. During the formation of myotomes, beginning in the cranial part of the embryo the amount of ChE in the engaged somite cells increases. At this time (Harrison 24-26) ChE-negative somites are found in the caudal part of the embryo. These somites become ChE-positive before they change into myotomes. 8. From the beginning the whole myoblasts are ChE-positive. Beginning with Harrison stage 35 the activity concentrates at the ends of the myoblasts near the segmental border. At this time a strong activity in the motor cells of the neural tube appears.