NATURAL HISTORY OF SOME TUBE-FORMING ANNELIDS. 229 



Nova Scotia specimens live among the rubble stone, where the violent action of the 

 waves frequently changes the position of the sand particles that fill the interspaces. 

 It is quite likely that the imperfectly and incompletely formed tubes of these small 

 Amphitrite are frequently broken into by the action of the waves. The reflex of 

 initiating the process of tube-forming may thus be brought into play frequently, 

 whereas in the larger, less exposed specimens the function of beginning the formation 

 of a tube may never be a necessity except once after the completion of the larval 

 period. A small portion of the tube of a large Amphitrite may serve as a stimulus 

 to the reflex of building more. With the removal of the entire tube, however, the 

 stimulus of an encircling substance is no longer present, and the annelid is not able to 

 originate an action which at one time was instinctive. 



The details of tube construction can be followed without difficulty by placing 

 a bare, or partially bare, specimen in a glass vessel with some mud and sand. I found 

 the smaller race much more favorable for study, as they could be confined in a micro- 

 scope stage aquarium at times when I desired to observe certain activities very mi- 

 nutely. 



The general method of tube-forming is as follows. The tentacles in great num- 

 ber extend in sinuous movement in all directions horizontally over the sand, the 

 tips appearing to feel their way through the water and along the bottom. Imme- 

 diately granules of mud and sand cling to the tentacles, but the tentacles continue 

 to extend until they seem to reach their full length. Then various ones begin to con- 

 tract and to bring along slowly and with seldom interrupted progress the adhering 

 masses of material. There is an entire lack of co-ordination in these movements; 

 many are at full extension, while others are at full contraction, and still others either 

 contracting or extending. Even single tentacles, for a brief period, manifest at the 

 same instant contraction in the proximal portion and extension in the distal portion. 



Examination with a hand lens shows that material is held here and there along 

 the tentacle in a long, shallow depression. Strands of mucus can be seen stretching 

 from the tentacle into and about the sand. Numerous small setae extend from the ' 

 tentacles, and undoubtedly these also help to hold material temporariby. In among 

 the setae and extending to about half their length are minute, active cilia. These, 

 with the setae, are found from the base of every tentacle, even to the tip of it. 

 The setae move their points slightly under varying muscular tension, and the cilia 

 lash constantly toward the proximal end of the tentacle. 



The material brought from all sides is collected in a ring behind the bases of 

 the tentacles and the gills. As fresh material is brought, the part already formed 

 as the beginning of a tube is pushed backward by the action of narrow ridges of muscle 



