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THE AMEBIC AN NATURALIST [Vol. XLYII 



although it could penetrate the egg and cause it to 

 develop parthenogenetically. 



A number of important experiments were tried to test 

 the correctness of this conclusion. The most striking of 

 these were those performed by Griinther Hertwig in cross- 

 ing different species. 



It is well known that the sperm of the frog will fertilize 

 the egg of the toad or of another species of frog, but the 

 resulting development proceeds for only a short time and 

 the egg usually dies in the blastulae stage. Giinther 

 Hertwig decided that if the influence of the sperm in 

 development was really destroyed by the intensive radium 

 treatments then such a spermatozoon would merely serve 

 as a parthenogenetic agent and the egg should develop in 

 a normal manner, yet be parthenogenetic. He used the 

 eggs of Bufo vulgaris (the common toad) and of Rana 

 veridis (the green water frog), and the sperm of Rana 

 fusca. He ran two sets of each kind of eggs ; one set was 

 fertilized by normal R. fusca sperm ; the other by sperm 

 which had been treated for two or three hours between 

 two capsules of mesothorium. The eggs fertilized by nor- 

 mal sperm did not develop beyond the blastular stage as 

 was expected, while those fertilized with the radiumized 

 sperm developed about normally and hatched from the 

 jelly and gave rise to swimming tadpoles. 0. Hertwig 



vulgaris with the sperm of Salamandra maLlata. The 

 sperm were treated for 2\ hours between two strong 

 mesothorium preparations. Poll had found that this 

 cross proceeded only as far as the blastular stage and 

 Hertwig confirmed this. 



When, however, the semen was treated for 2} hours a 

 different result was obtained. Many eggs failed to be- 

 come fertilized, some showed polyspermy, and only six 

 went normally. The chromatin of the sperm was thought 

 to be destroyed and the eggs went by parthenogenesis. 

 Loeb has found in the remarkably wide crosses he has 

 made on invertebrates and vertebrates that the products 



