Answer:
a long rodlike structure that develops dorsal to the gut and ventral to the neural tube. The notochord is composed primarily of a core of glycoproteins that are encased in a sheath of collagen fibers wound into two opposing helices. 
 
        
             
        
        
        
The red line is the wavelength 
The blue line is the amplitude
        
             
        
        
        
I think it’s all of the above because they can all be found in the air and in water sources