in the Fish Gallery of the Indian Museum. 15 



another, and differ from the three higher Classes, in 

 being without an amnion and allantois during embryo- 

 nic life. [An amnion is a special envelope formed for 

 the protection of the growing embryo. An allantois is 

 a special outgrowth of the hinder part of the gut of the 

 embryo, carrying with it blood-vessels, for the primary 

 purpose of respiration.] 



Fishes however differ from Amphibia in the form of 

 the limbs, which in Fishes — when they are present — are 

 fins, while in Amphibia — when present — they are seg- 

 mented limbs ending in digits. In Fishes again the 

 respiration is more completely aquatic ; for though there 

 are a few fresh-water fishes that have lungs in addition 

 to gills, the immense majority of fishes breathe, 

 throughout life, exclusively by gills : and though most 

 Amphibia when they leave the egg breathe entirely by 

 gills, and though some Amphibia keep their gills 

 throughout life, yet a majority of Amphibia, in the adult 

 stage, completely lose their gills, and even those that 

 do not lose them have lungs in addition. 



The Fishes, like the Amphibia and Reptiles, are 

 "cold-blooded;" that is to say, there is no nervous 

 mechanism for controlling the temperature of the body, 

 which therefore rises and falls with the temperature of 

 the environment. 



The form of the body among Fishes is generally 

 that of a spindle, a form that is admirably adapted for 

 cleaving a way through a resistant medium like water. 

 This form, which is almost universal among active- 

 swimming species, has necessarily become profoundly 

 modified, in various ways, to suit various other modes 

 of life. 



