448 CHARLES RUSSELL BARDEEN 



Bufo calamita, cf ] 



Bufo vulgaris, 9 [ Developed into larvie. 



Bufo vulgaris, cf 



Bufo calamita, 9 



Rana fusca, d' \ Developed to the "Stereo-blastula" stage but 



Bufo calamita, 9 / did not undergo gastrulation. 



Parthenogenetic development stimulated by 

 spermatozoon ceases in early cleavage stages. 

 In the P. puntatus cross the female pronucleus 

 acted as the segmentation nucleus. In the Bufo 

 calamita cross the second maturation division is 

 not completed but instead a cleavage nucleus is 

 formed. 



Triton alpestris, cf 

 Pelodytes puntatus, 9 

 Triton alpestris, cf 

 Bufo calamita, 9 



From these experiments it will be seen that when the sperma- 

 tozoon of one species enters the egg of a distant species the egg 

 may undergo cleavage, but as a rule development becomes abnor- 

 mal, before or during gastrulation and larval formation, and only 

 exceptionally proceeds to metamorphosis. The foreign sperma- 

 tozoon has the power of exciting cleavage, but as development 

 proceeds it either fails to furnish determinents requisite for devel- 

 opment or inhibits the action of maternal determinents which 

 might otherwise prove effective. By action of alterations in 

 temperature and of sugar solutions parthenogenic development 

 has been excited in the frog's egg. (Bataillon, '04). In these 

 experiments development extended to the blastula stage. Cleav- 

 age was incomplete so that the roof of the blastula alone showed 

 cytological segmentation. Bataillon follows Boveri in recog- 

 nizing two stages in early embryonic development, a 'promor- 

 phological' in which cell division is not followed by complex 

 morphological differentiation, and a ' metamorphological ' in which 

 complex differentiation takes place. The nuclei appear to play 

 a much more specific part in the latter than in the former stage. 

 It is the former stage that is initiated in the experiments on par- 

 thenogenesis in amphibia. 



While the maternal nuclei may govern the cleavage stages, the 

 experiments suggest that beyond these stages the maternal deter- 

 minants are of themselves incapable of stimulating development. 

 If the paternal determinents are of foreign origin or have been 

 injured, as by exposure to the X rays, development may proceed 



