DEVELOPMENT OF THE FROG'S EGG. 309 



In the preceding paper on "The Artificial Production of Spina 

 Bifida" it was noted that, apparently, the proanlagen and 

 anlagen of the embryo were restricted to the pigmented hemi- 

 sphere of the egg, that the raying of a small localized surface- 

 area of the yolk hemisphere or of the region of the quarter pro- 

 duced invariably the condition of spina bifida in the embryo. 

 It was noted in these embryos, however, that indications of the 

 destruction of cell groups or of definite areas of protoplasm in the 

 adult tadpoles were absent. No gross structural defects of organs 

 aside from the bifid character of the spinal cord were demon- 

 strable. Where the dosage of ultra-violet light ray energy was 

 sufficiently great, however, a mass of protoplasm equal in size 

 to the superficial area affected was extruded from the body of 

 the embryo. This was observed as well in this present experi- 

 ment. Under such conditions naturally the developed embryo 

 demonstrated both an organic and a structural defect. When 

 the dosage is reduced in amount, however, it is demonstrated 

 both by these and by the spina bifida experiments that the possi- 

 bility exists for the production of a developmental defect the 

 structural cause of which may not be present or recognizable in 

 the adult. The absence of atypical cytological characters as 

 well as organic defects and of exovates must force us to the con- 

 clusion that either such did exist for a longer or shorter period 

 during the development of the embryo and subsequently became 

 incorporated into the structure of the body as the result of an 

 elaborate but delayed chemical transformation, or that there 

 ensued upon the raying a transitory suspension of the physio- 

 logical activity of the cells affected with a later complete resump- 

 tion of that activity. Either conclusion must force us to pre- 

 sume, however, the presence of a chemical alteration either of 

 cell content or of cell mass as a direct result of the raying. 

 Indeed, it would be rather difficult to contend that no change 

 was brought about in the chemical composition of the protoplasm 

 in the area affected by the rays. 



Since it has been definitely proved that protein substances, 

 carbohydrates and lipins may be altered to some degree in their 

 chemical constitution by this form of energy, it does not appear 

 to be unreasonable to infer that one or all of the corresponding 



