262 



H. P. KJERSCHOW AGERSBORG. 



movements are alternated from "side to side. The lashing of the 

 anterior part of the body from side to side is relatively powerful 

 and a much more rapid progressive movement is effected over that 

 attained by creeping. The undulatory movements employed in 

 swimming start with the head being bent downward and sideways, 

 forming a wave-like twist in the side of the body-wall like that in 

 a blade of a propeller. This wave passes gradually toward the 

 posterior end (Figs. 3-4), and disappears when the animal makes 



FIG. 3. Photograph of Dendronotits gigantcus O'Donoghue in the act of 

 swimming; the head has returned from its bend to the right, and the twist-like 

 wave is shown in the side passing toward the posterior end. 



the next stroke to the opposite side. When the animal makes a 

 stroke to the right the posterior two thirds is bent so as to form 

 an angle of 45 with the anterior one third. But the posterior 

 part of the body also rotates about 45 from the vertical plane, so 

 that the left side with the foot forms a large wave which sweeps 

 posteriorly, while the anterior part of the body, in front of the 

 wave, is kept vertically. When the animal makes a stroke to the 

 left, the same phenomenon is repeated on the right side. An 

 animal may cover a distance of 30 cm. in a few seconds, making 

 side-strokes of about 45 a minute. 



The creeping method of locomotion was seldom employed. If 

 the animal was forced to the bottom of the dish, it would attach 

 itself to the substratum and commence gliding along imperceptibly. 

 Close observation brought to light, however, a succession of undu- 



