Abnormal Development of Toad Ova 5 



negative results he attibuted to the use of an apparatus from 

 which rays of merely moderate intensity could be obtained and 

 which could not be used for prolonged exposures. G. Bohn" has 

 reported the production of arificial parthenogenesis in Strongy- 

 locentrotus lividus by exposure to the rays of radium. 



The effects of the exposure of the fertilized eggs and the larvae 

 of Amphibia to the Roentgen and radium rays have been studied 

 by a number of investigators. P. K. Gilman and F. H. Baetjer" 

 have shown that the eggs of Amblystoma exposed to the Roentgen 

 rays exhibit a brief period of accelerated growth and then mark- 

 edly abnormal development. If the exposure is not too severe the 

 tadpoles may recover; if sufficiently severe they develop into 

 monstrosities and soon die. A. Schaper" obtained somewhat 

 similar results with frogs' eggs exposed to radium rays, although 

 he failed to find a period of accelerated growth immediately folio w^- 

 ing exposure. Schaper also found that regeneration of the tail 

 and limbs of Triton larvae is inhibited by exposure to radium rays. 

 The wound heals and a mass of cells is accumulated in the region 

 of the lost part but no specific regeneration takes place. O. Levy,^° 

 who has studied microscopically the specimens prepared by Schaper 

 just before his untimely death, comes to the following conclusions; 



1 In the period of cleavage of the ovum the rays may serve to 

 check or inhibit cell division but cause no cell degeneration. 

 Death may follow. 



2 In the period of formation and early differentiation of the 

 organs (generative self-assimilation) marked degenerative abnor- 

 malities appear in many of the organs, especially in the neural tube, 

 retina and nose. The optic lens, the pigment layer of the retina, 

 the aural vesicle, the chorda dorsalis, and the myotomes appear 

 comparatively little aff"ected. The heart is frequently rudimen- 

 tary. The tubules of the pronephros are frequently dilated. In 

 general, the eff^ects are the most serious in those tissues in which 

 growth and complex diff^erentiation are normally most rapid. 



''G. Bohn: Comptes Rendus de TAcad. des Sciences, Paris, cxxxvi, pp. 1012, 1085, 1903. 

 ^*P. K. Gilman and F. H. Baetjer: Amer. Jour, of Physiology, x, p. 222, 1904. 

 '^'A. Schaper: Anat. Anzeiger, xxv, p. 298, 1904; Deutsche med. Wochenschrift, xxx, 1904. 

 ^"O. Levy: Archiv f. Entwicklungsmechanik, xxi, p. 130-152, 1906. 



