CYCLOSTOMATA 



415 



Habits and Behavior 



The animal is a rather inebriate type of swimmer because it is 

 long and slender and does not possess paired fins. It winds its way 

 through the water and occasionally comes to rest by attaching 

 itself to a rock by means of an oral funnel. 



External Structure 



In most respects the Atlantic lamprey, Petromyzo7i marinus, and 

 the Pacific form, Entosphenus trident aUis, correspond quite closely 

 in structure and make excellent representatives for study of the 

 group. The following account will fit them generally. They may 

 reach a length of three feet and three inches. The color is rather 

 variable but might be expressed as being a variegated olive brown. 

 Along the length of the lateral axis of the body are distributed 

 sensory organs. There are two dorsal fins and a caudal fin, but no 

 paired fins. At the anterior end of the animal is the mouth with 

 the luccal funnel extending from it. This funnel is provided with 

 ehitinous teeth used in rasping through the body wall of the host 

 fish. The annular cartilage supports the margin of the funnel and 

 holds it open. Along the margin is a fringe of papillae. The mouth 

 lies at the bottom of the funnel. In the floor of the mouth is a 

 plungerlike tongue supported by a cartilage and bearing teeth. 

 There are seven uncovered gill slits along each side of the anterior 

 portion of the body. In front of the gills on each side of the head 

 is a poorly developed eye. It has no lid, simply being covered with 

 transparent skin. In a middorsal position on the head is located 

 the single nostril which leads into an olfactory chamber, and on 

 ventrally as a pituitary pouch or caecum. The anus is located in 

 the midventral line a short distance anterior to the tail. Immediately 

 behind it is the urinogenital opening at the tip of a papilla. The 

 papilla is larger in the male specimens. 



Internal Structure 



The muscular system is quite primitive. It is principally a series 

 of zig-zag myotomes along the length of the body very similar to 

 those in Amphioxus. A large lingual muscle is differentiated for 

 moving the tongue, and several bundles of muscular tissue radiate 

 through the wall of the funnel to expand and contract it. 



