THE NECTURUS 



INTRODUCTION 



This member of the amphibian group is a very desirable 

 form for dissection, since it represents a rather simple 

 tetrapod. It is a curious mixture of specialization and 

 primitiveness with the latter predominant. The lungs may 

 have been better developed at one time than they are at 

 present, but now they are very small, inefficient and unable 

 to carry on the work of respiration without the aid of gills. 



A number of the amphibia have been left in the halfway 

 position of being neither water nor land animals, and these 

 possess both lungs and gills throughout life. Due to the 

 possession of a moist glandular skin, the amphibia have 

 never been able to separate themselves from water to the 

 degree possible in forms with a dry skin. In order to 

 secure the fertilization of their eggs most amphibians have 

 to go to water to deposit them, although a few have de- 

 veloped so far into land animals, that the metamorphosis 

 takes place in a very short time after hatching, thus ena- 

 bling them to lay their eggs in damp places. A few have 

 developed so that they are able to bring forth their young 

 alive. All others must make an annual pilgrimage to 

 water for egg laying. A small number have lost both 

 gills and lungs and must depend on other parts of their 

 bodies for the purification of their blood. Pharyngeal 

 passages, richly supplied with blood vessels, help in the 

 aeration in the lungless forms. 



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