176 THE COURTSHIP OF ANIMALS 



sequence to this also obtains. That is to say, as has 

 already been remarked in the case of the Mammals and 

 the Birds, the new features first appear in the males, 

 leaving the females and young of both sexes unmodified. 

 A singular illustration of this is afforded by some 

 of the Rays, or Skates, as they are often called. In 

 the Thorn-backed Ray {Raia clavata) the teeth of 

 the adult male are sharp-pointed and directed back- 

 wards, while those of the female are broad and flat, 

 forming a sort of mosaic or pavement. The young male 

 agrees with the female in this respect. In the Common 

 Blue Skate {Raia baits) the teeth are pointed in both 

 sexes, though more so in the adult male. In the 

 Spotted Skate (Raia maculata) the teeth are fully 

 pointed in both sexes. Here, then, the normal course 

 in the evolution of new characters is followed, but it is 

 remarkable that the teeth, which are so intimately 

 related to the capture of food, should be thus affected. 

 Whether the change of teeth is associated with a change 

 of food, or whether neither pointed nor pavement teeth 

 affect the feeding, is unknown. 



Still more remarkable is the case of the Double-eyed 

 Fish {Anableps). In this fish there is an intromittent 

 organ in the shape of a tube which is formed by a 

 continuation of the urinogenital ducts down the front 

 of the anal fin. In the hinder half of this organ a 

 bend is made either to the right or left. Out of seven- 

 teen males, this bend was to the right in eleven, to 

 the left in six. Further, there is a small fleshy 

 tubercle at the side of the anal fin-ray, at the middle 

 of its length. When this prominence is on the left 

 side, the organ bends to the right ; when it is on the 

 right, the bend is to the left. In the females the genital 



