406 THREAD-CAPSULES. 



external edge beset with a fringe of delicate vibratile 

 cilia, by whose constant action not only were the 

 floating atoms in the water hurled in a rapid and 

 regular current along the edge, but the spires of 

 ribbon themselves were made to swim through the 

 water, principally with a slow gyratory motion, suffi- 

 ciently perceptible even to the naked eye. 



On subjecting some of the whorls to the com/presso- 

 Hum, an immense number of yellowish granules were 

 discharged from the brown part, while the pellucid 

 border displayed the filiferous capsules in considerable 

 number, pointing towards its outer edge. They are 

 club-shaped, or almost fusiform, with one end the 

 larger, varying from -^ to -^ th inch in length ; the 

 contained thread occupies a slender linear cavity? 

 extending about two-thirds through the length, and is 

 thence continued as a line of almost invisible tenuity. 

 (See Plate XXVIII., fig. 17.) When the thread is 

 forced out by pressure, it sometimes extends to -g^-or 

 even -^ of an inch. The basal portion of the thread, 

 for a length about equal to that of the capsule, is zig- 

 zagged, and each angle of the zigzag is furnished 

 with a short bristle, projecting in the direction of the 

 joint from which it springs. There are about four or 

 six angles, the first being removed a little from the 

 tip of the capsule. (See fig. 19). 



The capsules of the tentacles are much smaller, 

 being from ^ to y^tli inch in length, and more pro- 

 perly linear than any I have yet seen. (Fig. 18). I 

 could not force the ejection of the thread. 



In the ribbed coriaceous skin that surrounds the 

 mouth, the capsules are the most developed of all. 



