CHORDATA 



279 



ducts, and the urinary ducts from the kidneys. Dorsal to the rec- 

 tum in the abdominal cavity is a peculiar gland, the rectal gland. 

 The fundamental structure of the skates or rays is the same 

 as that of the sharks ; the chief difference lies in the general 



Fh;. 288. Ra/a maculata, a skate. A, dorsal surface, showing spiracles just posterior to 

 the eyes ; B, ventral surface, anterior end, showing nasal pits and mouth. (From Sh 

 and MacBride's Zoology.) 



shape of the body, which is clue to the great flattening dorso- 

 ventrally, and the enormous development of the pectoral fins, 

 which spread out laterally from the tip of the head to beyond 

 the pelvic fins (Fig. 288). This brings the gill clefts to the 



