298 W. M. BALDWIN. 



neural tube-halves. Because of its lateral position and close 

 relationship to one of these halves it might exert, however, a 

 restraining influence upon the rate of migration of the tube-half 

 of the corresponding side of the egg. This retardation of the 

 shifting of the hemineural anlagen on the affected side induced a 

 correspondingly exaggerated migratory process in the anlagen 

 upon the unaffected side of the egg. As a result of this loss of 

 coordinated, migratory movement, the anlagen upon the affected 

 side had not yet reached the median plane before fusion took 

 place with the unaffected anlagen by reason of their exaggerated 

 migration. The normal angularity of the hemineural long-axis 

 persisted more or less completely, therefore, in the adult tadpole 

 as a result of this process. This was expressed by the curvature 

 of the trunk invariably towards the affected side. The location 

 of this flexure, as was stated above, was directly dependent upon 

 the segmental level of the affected area of protoplasm. 



It is a singular fact that the histological sections failed to 

 demonstrate a single gross or microscopic defect in these embryos. 

 The viscera developed normal in shape and in size. No defects 

 could be recognized in the muscle segments. The mass of these 

 in the concavity of the flexure was estimated roughly to be the 

 same as that of the corresponding segments on the convex side 

 of the body though their shape was necessarily distorted to fit 

 the concavity. The yolk mass of the trunk of the embryo was 

 completely utilized in the differentiation of the tissues and in the 

 metabolical processes of the embryo. There was no evidence at 

 any time that a portion of this yolk mass had been rendered 

 completely inert by the rays and consequently excluded from 

 participation in the normal chemical developmental processes 

 of the body. 



The action of the rays inferentially, therefore, had not induced 

 such chemical changes as would permanently eliminate the sub- 

 stances affected from participation in .the normal organo-genetic 

 or somatogenetic processes. But the rate of chemical modifica- 

 tion of these substances in participation in the normal metabolical 

 processes of the embryo was, however, retarded. We may find in 

 this retardation of chemical participation additional evidence 

 for the causation of the check of the normal lengthening process 



