III. 3 ELECTRICITY AND MAGNETISM 93 



tube surrounded by a coil, could any definite relation be satis- 

 factorily made out between the direction of the first furrow and 

 that of the current. Indeed, though intrinsically interesting, 

 the experiments throw no particular light upon the problem of 

 development. Rather should they be classed with the investiga- 

 tions of Verworn and others upon the behaviour of Protozoa 

 in the electric current, investigations which promise to contribute 

 to the understanding of the structure and movements of living 

 substance. It may be noted here that Roux has himself 

 produced these polar areas on such structures as the heart and 

 gall-bladder of the Frog and other vertebrates. 



LITERATURE 



C. DARESTE. Recherches sur I'influence de 1'electricite sur revolution 

 cle 1'embryon de la poule, Cotnptes Bendus, cxxi, 1895. 



U. Rossi. Sull' azione dell' elettricita nello sviluppo delle uova 

 clegli Anfibi, Arch. Ent. Mech. iv, 1897. 



W. Roux. Ueber die morphologische Polarisation von Eiern und 

 Embryonen durch den electrischen Strom, sowie iiber die Wirkung des 

 electrischen Stroins auf die Richtung der ersten Teilung des Eies, 

 S.-B. kais. Akad. Wiss. Wien, ci, 1891, also Ges. Abh. 25. 



B. C. A. WINDLE. On certain early malformations of the embryo, 

 Joum. Anat. and Phi/s. xxvii, 1892-3. 



B. C. A. WINDLE. The effects of electricity and magnetism on 

 development, Joum. Anat. and Phys. xxix, 1895. 



4. LIGHT 



As Roux pointed out long ago in the case of the Frog, light 

 exercises no directive influence upon the development of the 

 ovum. Blanc, indeed, has attempted to prove that the direction 

 of the embryonic axis in the egg of the Hen may be made to 

 depend upon the direction of the incident light-rays, but the 

 experiments are hardly conclusive. The method employed was 

 to blacken the shell of the horizontally placed egg with the 

 exception of one spot to right or left of the blastoderm. On 

 this spot a beam of light was kept directed during incubation. 

 In some cases, but not in all, the embryonic axis was found to 

 deviate from its normal position at right angles to the long 

 axis of the shell. Further, the head of the embryo might be 

 turned towards or away from the source of light. There was 



