//. THE AMPHIBIA 

 A, The Normal Development of the Amphibia 



1. NOTES ON THE BREEDING HABITS 

 OF SOME COMMON AMPHIBIA 



Natural breeding on the part of different species of the Amphibia covers all the seasons 

 of the year, in the various latitudes. The one characteristic feature of all but a very few 

 specialized forms is that breeding occurs in or near water regardless of the habitat during 

 the balance of the year. In general, the Amphibia lay their eggs and then desert them. 

 This means that there is a very high mortality and in order to survive, the race must 

 produce a great excess of eggs. It has been estimated (Smith: Science 1947, v. 105, 

 p. 619) that the maximum number of eggs layed by any amphibian species is probably in 

 the neighborhood of 35, 000. It is interesting that the high numbers are layed by the pre- 

 dominantly aquatic Anura while among the Urodela the number of eggs layed may be less 

 than 100, in certain species. The aquatic environment is apparently the more hazardous 

 when compared with the mildly damp environment where one occasionally finds Urodele 

 eggs- 

 Regarding the insemination of the eggs, the frogs shed their products into the water si- 

 multaneously during amplexus; many of the toads similarly shed their gametic products 

 but the eggs are layed in strings and the male inseminates each egg as it emerges from 

 the cloaca. Finally, among the Urodela it is necessary for the female to pick up sperma- 

 tophores and to take them into her cloaca and genital tract where the eggs are fertilized 

 before being layed. Thus there is considerable variation in the breeding procedure among 

 the various species of Amphibia. 



There are a number of forms which, because they are relatively common, are likely to 

 be available for use in our laboratories. For this reason there is presented below a 

 table showing the common name, location, breeding periods, and egg production of these 

 forms. 



BREEDING HABITS OF SOME COMMON AMPHIBIA 



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