 major advantages of the use of aquatic animals , such as trout , english sole , or sea urchins , for studying the mechanisms of reproductive toxicology are discussed . 
 the remarkable synchrony of differentiation of gametes in large quantities for detailed morphologic and biochemical measurements enables research not readily done on mammalian nonseasonal breeders . 
 structural differences such as the absence of a fibrous sheath in the more simple structure of fish and sea urchin sperm flagella facilitates comparative study of the mechanism of action of microtubules in flagella movement and the coupling of mitochondrial energy production to microtubules movement.imagesfigure 1.figure 2.figure 3.figure 4.figure 6.figure 7 . 
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