1919] Cort: The Cercaria of the Japanese Blood Fluke 503 



pushes the ends of the duets of the cephalic glands with their spines 

 well back into the middle of the sucker and produces a cavity at the 

 anterior tip lined with the surface spines. It is this rolling-in action 

 of the anterior tip which makes suction possible. 



The locomotion on a substratum of the eercaria of S. japonicum con- 

 sists of an alternate taking-hold and loosening of the ventral sucker 

 and the anterior tip. In initiating locomotion on a substratum the 

 eercaria takes hold with its ventral sucker and stretches out its body 

 to about one and one-half times the normal length. The extended 

 body may sway backward and forward and reach around as if it 

 were exploring. At greatest extension the body, which at this time 

 has a w'idth no greater than the width of the tail, bends over and the 

 anterior tip takes hold, then the ventral sucker is loosened and is pulled 

 forward to take hold just back of the anterior tip ; this causes the body 

 to arch up. After the ventral sucker takes hold the anterior tip is 

 loosened and the preacetabular region is again extended and takes hold. 

 Each time the body is bent up for the ventral sucker to take a new 

 hold the tail is vibrated. Quick repetitions of this movement produce 

 a fairly rapid locomotion. The bending-up of the body and the taking 

 hold by the ventral sucker are accomplished so quickly that the eercaria 

 gives the impression of moving across the surface by a series of jumps. 

 Even if the anterior tip does not get a hold, as is often the case in 

 movement on a smooth surface, the eercaria will make progress, since 

 the ventral sucker, aided by the vibration of the tail, will gain a hold 

 in advance of its previous hold. At the initiation of the movement 

 when the anterior end is at its greatest extension the openings of the 

 ducts of the cephalic glands with their spines are just at the anterior 

 tip, but when the worm bends over to take hold the anterior tip is 

 rolled in, so that the openings of these ducts point toward the center 

 of the oral sucker and the surface which catches hold is covered with 

 spines. 



Certain of the activities of the eercaria of S. japonicum show direct 

 correlation with penetration into the human host. The tendency of 

 the eercaria to adhere and move on the surface of any object with 

 which it comes in contact would tend to bring it into relation to this 

 host. In several instances cercariae were watched when attached by 

 their ventral suckers to pieces of snail tissues. "When in this position 

 the preacetabular region reaches out in all directions in an exploring 

 movement. This movement, combined with the rhythmical pushing 

 out and rolling in of the anterior tip made the cercariae look as if 



