982 THE AMERICAN NATURALIST. . [Vor. XXXV. 
the field of direct stimulation and contact is evident. The 
animal crawls along the bottom of a jar with the ventral sur- 
face uppermost almost as often as in the other position. It 
is unable to support itself free in the water, although it 
often drops from the surface to the bottom, making the usual . 
crawling movements during the descent. During all forward 
movement the head is continually making rapid searching 
movements in all directions. 
Backward movement is accomplished in a manner entirely 
different from that just described for forward locomotion, vtz., 
by muscular contractions. 
The muscular activities concerned in backward locomotion 
consist of a series of peristaltic waves. A contraction of the 
circular muscles near the posterior end occurs, and the end is 
thrust backward ; then a wave, consisting of strong contractions 
of the longitudinal and relaxation of the transverse muscles, 
producing a shortening and thickening of the region affected, 
begins at the posterior end of the body and travels forward. ` 
The whole process is quickly repeated, and in continued back- 
ward movements three or four of these peristaltic waves may 
be visible on the body at one time. On a smooth surface like 
glass these movements are rather ineffective, but it is easy to 
see how, under natural conditions, the posterior end of the body 
becomes more or less completely fixed as soon as increase in 
size begins and the other portions are drawn back to it. 
The body is extremely contractile, and different parts are 
capable of independent contraction. In the reassumption of 
the extended position after contraction, the extension usually 
begins at the anterior end and proceeds backward along the 
body as the head advances. 
Movements of the proboscis within the rhyncoccel are very 
common.  Contraction of the circular muscles in the posterior 
portions of the body causes the proboscis to be thrown for- 
ward, and, conversely, extension of the head region forces it 
backward. In general the proboscis, together with the fluid 
of the rhyncoccel, tends to occupy the region of least pressure. 
The relation of the cilia to the different movements 1s 
interesting. During forward movement the cilia are in active 
