SEA-ANEMOMES : THEIR WEAPONS 41S 



abruptly) attenuated, and runs on for the remainder of 

 its length as an excessively slender wire of equal diam- 

 eter throughout. In the short ecthorcea of Sagartia, the 

 attenuated portion is obsolete. 



"It is chiefly upon this ventricose basal portion that 

 the elaborate armature is seen, which is so characteristic 

 of these remarkable organs. For around its exterior wind 

 one or more spiral thickened bands, varying in different 

 species as to their number, the number of volutions made 

 by each, and the angle which the spiral forms with the 

 axis of the ecthorceum. The whole spiral formed of these 

 thickened bands is termed the screw or strebla. 



"In the ecthorcea emitted by chambered cnidce from the 

 craspeda of Tealia crassicornis, the screw is formed of a 

 single band, having an inclination of 45 to the axis, and 

 becoming invisible when it has made seven volutions. In 

 those from the same organ in S. parasitica, we find a 

 screw of two equidistant bands, each of which makes 

 about six turns twelve in all having an inclination of 

 70 from the common axis. In those similarly placed in 

 Cyathina Smithii [now under your observation], the strebla 

 is composed, as you may perceive, of three equidistant 

 bands, each of which makes about ten volutions thirty 

 in all with an inclination of about 40 from the axis. In 

 every case the spiral runs from the east toward the north, 

 supposing the axis to point perpendicularly upward. 



"Sometimes, especially after having been expelled for 

 some time, the wall of the ecthorceum becomes so attenu- 

 ated as to be evanescent, while the strebla is still distinctly 

 visible. An inexperienced observer would be liable, un- 

 der such circumstances, to suppose that the screw, when 

 formed of a single band, as in T. crassicornis, is itself the 



