METABOLIC GRADIENTS OF VERTEBRATE EMBRYOS. 21 







eggs tend to develop abnormally if they are not turned during 

 incubation or if they are incubated in the vertical position. 

 Few details are, however, furnished as to the types of abnor- 

 malities so induced . They are stated to result from the adherence 

 of the embryonic membranes to the shell. 



Several workers have reported induction of teratological de- 

 velopment in the hen's egg through exposure of the eggs to the 

 electric current or a magnetic field (Lombardini, '68, Maggiorani, 

 '84, Windle, '91, '93, '95). I have not been able to obtain these 

 publications except two of Windle's but it appears that very few 

 details were given in them of the types of abnormalities obtained. 

 Probably the teratological action really resulted from the products 

 of electrolysis rather than directly from the current or magnetic 

 fields. Windle found a high percentage of malformed embryos 

 with defective areae vasculosse but Maggiorani reported an 

 excessive vascularization of the yolk sac with arrested develop- 

 ment as a result of incubating eggs between two powerful 

 magnets. 



There has been some investigation of the action of X-rays and 

 radium emanations on the development of the chick. Gilman 

 and Baetjer ('04) exposed hen's eggs to X-rays ten minutes a day 

 for four successive days and noted certain abnormalities de- 

 formed occipital region, retarded eyes, membranes adherent to the 

 embryos, and deformations of the limbs. Tur ('04) subjected 

 hen's eggs continuously to radium placed on the outside of the 

 shell during periods of incubation varying from 24 to 70 hours. 

 After 24-28 hours of such treatment, blastoderms of normal size 

 were found, but the area pellucida was reduced, and only the 

 posterior part of the primitive streak was in, evidence, the 

 anterior part having been reduced to an irregular mass. After 

 45 to 70 hours of incubation under radium emanation blasto- 



/ 



derms without visible embryos were obtained. In some cases 

 the area vasculosa was present and more or less normal in 

 appearance; in other blood and blood vessels were lacking and 

 the area pellucida was greatly reduced. Sections of such blasto- 

 derms in the region where the embryo was to be expected revealed 

 the presence of a flattened inactive ectoderm and a thickened 

 proliferating entoderm showing numerous mitotic figures. Tur's 



