314 THE OCEAN WORLD. 



Nature had not thought of piercing the body with an opening suffi- 

 ciently large for each one to see what was passing in the interior. 

 The creature which now occupies our attention would surely have 

 satisfied the demands of our critic : its body is, metaphorically 

 speaking, a house of glass. 



Fig. 126. Salpa maxima magnified (Forsk). 



In order to move itself, the Salpa has recourse to a singular artifice. 

 It introduces water into its body through a posterior opening, furnished 

 with a valve, which it expels by an anterior outlet situated near the 

 mouth. It is thus pushed backwards, and swims, as it were, by recoil. 

 Moreover, it swims with its belly upwards. All the elements of a 

 chain of Salpas act in concert ; they contract and dilate simultaneously ; 

 they advance as a single individual. One of them floats on the surface 

 with the undulations of a serpent, so that among sailors they have 

 gained the appellation of sea-serpents. These long, living trains 

 abound in the Mediterranean, principally towards the African coast, 

 and in the Equatorial seas. They are inhabitants of the open sea, 

 and live immerged at considerable depths ; but when the nights are 

 calm they show themselves on the surface. As they spread them- 

 selves abroad with a strong phosphorescent light, they resemble long 

 ribbons of fire, unrolling their long waving lines in spite of the waves, 

 as in Fig. 127. What wonders they see who go down into the great 

 deep ! What sights are reserved for the navigator who traverses the 

 Tropical seas during the silence of night ! 



When a chain of Salpas is drawn from the water, the rings separate, 

 and they can no longer be made to adhere. The social bond has been 

 dissolved by a superior force. 



Salpas are sometimes met with, isolated and solitary, whose exterior 



