274 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



gastrula stage, 13 unfertilized punctured eggs were also in the 

 gastrula stage and 4 more eggs were developing abnormally. 

 On the fourth day, 8 of the parthenogenetic eggs had good 

 medullary folds and 4 had irregular folds. On the sixth clay 

 most of the fertilized eggs hatched and 8 of the parthenogenetic 

 eggs hatched also. Of these latter, 4 were developing regularly 

 and 4 irregularly. Those that had not hatched were abnormal. 



On the eighth day, the larvae arising from the fertilized eggs 

 were swimming. Among the larvae arising from the unferti- 

 lized punctured eggs only 3 were normal, and their develop- 

 ment was slightly retarded, perhaps one day. In addition, 6 

 parthenogenetic larvae were abnormal but still alive. 



On the thirteenth day, 2 of the parthenogenetic larvae were 

 feeding and these were the only ones which survived definitely. 

 The other parthenogenetic larvae all died during the next few 

 days. Of the 2 surviving larvae, one went through meta- 

 morphosis after five months. When it died, the tail was almost 

 completely absorbed (Fig. 76). Its death was probably acci- 

 dental. The other lived (Fig. 77) a month longer and formed 

 small hind legs, but died in the tadpole stage. A repetition of 

 these experiments by the same authors showed that only the 

 eggs of Rana sphenocephala and R. pipiens produce tadpoles 

 when punctured, while the unfertilized eggs of R. silvatica, 

 Chorophilus feriarum, and of Bufo americanus only begin to 

 segment but die before the tadpole stage when they are 

 punctured. 



As far as the effect of puncturing the egg is concerned, it 

 may be comparable to the effect of agitation upon the starfish 

 egg. The latter forms a membrane as an effect of agitation 

 and it may be that the destruction of the surface layer of the 

 frog egg is the essential feature in this "traumatic"' partheno- 

 genesis. While the spermatozoon causes the destruction of the 

 cortical layer of an egg by a chemical substance (a "lysin"); 

 and while the same can be accomplished in the egg of some 



