DEVELOPMENT OF THE FROG S EGG. 297 



processes of which it normally was a part but, in addition, caused 

 its presence to act as a mechanical hindrance to the developmental 

 shifting of anlagen. 



Studies of the action of ultra-violet light rays have produced 

 proof that proteins, carbohydrates, and lipins may be chemically 

 altered by means of this form of energy. To review the experi- 

 mental results briefly: Massol and Kluyver have ascertained 

 that starches may be altered, and Stoklasa, Zdobnicky, Chau- 

 chard and Mazone, and Pougnet that they may be ultimately 

 broken up. Diastase may be liberated in plants (Maquenne and 

 Demoussy). Bierry, Henri, and Ranc have inverted cane sugar. 

 Agulhon, Maurain and Warcollier, and Raybaud ' presented 

 evidence that the action of enzymes in the presence of oxygen 

 was weakened and destroyed by ultra-violet light. Furthermore, 

 albumen may be coagulated (Bovie) and the iodine content of 

 fats may be lowered (Roemer and Sames). Thus we may 

 reasonably infer that ultra-violet light rays are capable of bringing 

 about certain chemical modifications of the protoplasm of the 

 cell to all or to part of which we may attribute the abnormality 

 in development noted. The . evidence is lacking at present, 

 however, which might enable us to associate this developmental 

 result with a specific alteration of protein, of carbohydrate, or 

 of lipin. 



It was pointed out in the preceding paper that the superficial 

 mass of altered protoplasm situated between the approximating 

 neural ridges prevented their normal fusion with the consequent 

 formation of a complete neural tube. The condition of spina 

 bifida resulted, therefore, as a direct result of the mere mechanical 

 interruption of this process. The action of the altered proto- 

 plasm was owing entirely to its passive function as a mass which 

 mechanically interfered with the medianward, migratory move- 

 ment of the hemineural anlagen. At least, in this one factor 

 could be found sufficient evidence as the causative condition of 

 this abnormality. 



In the present instance of the U-shaped embryo, however, the 

 inert mass was located lateral to and above the level of the hemi- 

 neural anlagen. It could not, therefore, by virtue of inter- 

 position mechanically interfere with the approximation of the 



