168 CARNEGIE INSTITUTION OF WASHINGTON. 



right (like a right-handed screw). The worms can not be induced to swim 

 with the anterior end ahead, not even small immature worms. Neither 

 could the anterior ends of worms, which had set free the posterior sexual ends, 

 be stimulated to swim with the anterior end ahead. The sperm cells swim in 

 spiral paths, rotating to the left. The sperm cells are large and swim rela- 

 tively slowly so that their movements may be readily made out. They also 

 have the habit of frequently attaching themselves by the end of the flagellum, 

 whereupon they swing in large circles to the left, the head of the sperm de- 

 scribing the circle while the end of the tail is in the center of the circle. They 

 turn to the left, that is, when fastened to the surface of the slide ; when fastened 

 to the under surface of the cover-glass they travel to the right as one looks 

 at them through the microscope. The reason for this is obvious when one 

 remembers that the sperm head revolves on its long axis to the left when 

 swimming freely. This observation is of great value in this connection for 

 it serves as a key to interpret the movements of many kinds of sperms that 

 swim too rapidly to enable one to see directly the direction of rotation; all 

 that is necessary now is to observe those sperm cells that are anchored and 

 determine in what direction they swing, and whether they are attached to 

 the surface of the slide or of the cover-glass. The behavior when swimming 

 freely may then be inferred. 



The fertilized eggs become ciliated 10 hours after fertilization and swim 

 at first in an uncoordinated manner. Later they swim in a well-coordinated 

 manner, rotating to the left on their long axis. At first the path is a straight 

 line, but a spiral path soon develops and after 6 days the spiral becomes very 

 marked, the spiral turns having a diameter from one to three times the 

 diameter of the larva. Along with a constant increase in the width of the 

 spiral as the larva develops there is a constant decrease in the length of the 

 spiral until the latter becomes practically zero and forward progression stops. 

 The larva then swims around in small circles in the same spot; it soon sinks 

 to the bottom and adopts crawling as a method of locomotion. 



Organisms like the Atlantic Palolo are particularly valuable in studying 

 spiral movement because three different stages of its existence move in 

 spirals. An important question is: Do the different stages in such animals 

 turn in the same direction; and if not, as in the Atlantic Palolo, where the 

 mature worm turns to the right and the sperm and larva to the left, what 

 relation is there between swimming with the posterior end ahead and reversing 

 the direction in which the worm as a larva turned? 



The movements of Salpa democratica and S. fusiformis were also studied, 

 for the method of locomotion in these animals differs altogether from that 

 of any other organism which is known to swim in spiral paths. The chain 

 form of Salpa democratica rotates on its long axis to the right in swimming 

 ahead in a close spiral path. Young detached individuals (5 mm. to 8 mm.) 

 swim in very open spirals soon after detaching themselves from the chain, 

 making very little forward progress. Older individuals and young individ- 

 uals detached for a time swim in closer spirals and make more progress forward. 

 The nucleus is on the inner side of the spiral. The solitary form was not 

 studied carefully enough to make definite statements about their movements. 



Salpa fusiformis, solitary form, rotates to the right whether swimming 

 forwards or backwards. They swim in large, open circles, making little 

 forward progress. They rotate with the nucleus on the outer side of the 

 spiral. Further details will be given in a paper on spiral movements. 



