NATURAL HISTORY OF SOME TUBE-FORMING ANNELIDS. 233 



from physical injuries. While the outward and inward, almost simultaneous, wav- 

 ing of the gills is not going on, two other means of creating currents in the water are 

 employed. One is an alternate spiral contraction and the reverse spiral extension 

 of an entire gill, this operation taking place independently of similar spiral movements 

 in any other gill. The other movement is a much less noticeable waving away from 

 and toward the central stem of the minute branches themselves. The slow waving 

 of the gills, the spiral contraction, and the movement of the minute branches may 

 all occur at the same instant. During locomotion these minute activities are un- 

 necessary and are not performed. When disturbed outside its tube the animal coils, 

 with the dorsal surface outermost, contracting the gills close against the body. 



Locomotion outside the tube, either when the animal is wholly outside or only 

 partly out, is accomplished by the creeping movement of the ventral rami of the 

 five pairs of parapodia on the anterior five trunk somites, aided by a pair of large, ven- 

 tral palps. Posterior from the fifth pair of parapodia the ventral ramus disappears, 

 except for the basal portion, which is transformed into a pad-like secreting surface 

 for the material that forms the leather-like lining of the tube. The dorsal ramus, 

 the cirrus of which becomes the gill-protecting organ already described, remains, but 

 does not aid in locomotion except inside the tube, where their horizontally extended 

 seta can reach a point of leverage. Sometimes when Diopatra is forced from the 

 tube it immediately begins a series of spiral contractions of extreme rapidity, 

 made with the tail in advance. It is altogether likely that this movement is 

 quite abnormal, as it is not progressive, and occurs only at this time of extreme 

 stimulation. 



Diopatra can be forced to leave its tube by thrusting any pointed object against 

 the posterior end or the head. Frequently a great quantity of mucus comes out at 

 the same time. On reaching the water the animal usually goes through the contor- 

 tions just described, although in some instances it simply creeps away. Whenever 

 there is suitable material at hand the animal begins at once to form a tube by crawling 

 first under a mass of sand and organic waste. Using this as a foundation it reaches 

 out, testing the surrounding objects tactually with its two pairs of lateral and its mid- 

 dorsal cephalic cirri, and with its pair of large ventral palps. The one pair of eyes 

 are placed dorsally, and could not be of much service for vision immediately in front, 

 unless the objects extended above the level of the eyes. When an object of suitable 

 size is discovered the ventral pair of later cirri test it more carefully, and if the par- 

 ticle proves fight and small, it is picked up by the strong ventral pair of palps. If 

 the object is too heavy to be moved by this means, the mandibles are thrust out to 

 grasp it. The gravel or piece of shell is carried backward by the contraction of the 



