354 



that happened to be spawning at the same time, and note the possibility and 

 character of impregnation, the development of the hybrids and the fate 

 of developing embryos. 



The writer wishes to express his sincere thanks to Prof. Charles B. 

 Davenport for privileges enjoyed at the Miami Laboratory, Cold Spring 

 Harbor ; to Hon. Geo. M. Bowers and Supt. Francis B. Sumner for privileges 

 at the United States Fish Commission Laboratories at Woods Hall, and to 

 the trustees of the Elizabeth Thompson Science Fund for a grant that made 

 it possible incidentally to gather some of the data included in this report. 



HISTOEICAL. 



With one exception, to be noted later, it is possible to impregnate the 

 eggs of any of the species tried, with the sperm of any other species tried, 

 although they belonged to widely separated orders. Isolated instances of 

 equally, or even more distinct crosses have been recorded. Api>ellof {'94) 

 made the following crosses among fishes : 



Pleuronectes platessa $ 

 X 

 Gadus morhua (J' 

 Labrus rupestris 9 



X 

 Gadus morhua cf 



In each of these the species belong to distinct orders. A portion only of 

 the eggs were impregnated. A few showed irregularities in cleavage, and 

 were presumably polyspermic. The European Amphibia have been exten- 

 sively hybridized by Pfliiger ('82) and by Born ('83). The former succeeded 

 in impregnating the eggs of Rana fusca with the sperm of both Triton 

 alpestrls and Triton taeniatus, i. e., an Anuran with a Urodele. The seg- 

 mentation, however, was irregular so that all the eggs were probably poly- 

 spermic. [Morgan ('93) succeeded in impregnating the eggs of Asterias with 

 the sperm of Arhada. He obtained normal cleavage, the larvae developing, 

 to blastulfe and gastrulse. His experiments were carefully repeated by 

 Driesch ('98) without result. Mathews ('01) believed Morgan's results 

 were due to parthenogenesis induced by shaking the eggs. Loeb ('03), work- 

 ing with the Pacific Coast Echinoderms, found it impossible under normal 

 condition to fertilize the eggs of Strongylocentrotiis purpnratiis with the 



