SEA-AOTEMONES : THEIR WEAPONS. 425 



tremity runs off to a finely attenuated point, the wliole 

 of the spire visible even to the last, the whole bearing 

 no small resemblance to a multispiral shell ; as one of 

 the Cerithiadm or Turritelladm. The eothormim is dis- 

 charged reluctantly from this form, and I have never 

 seen an example in which the whole had been run off. 

 So excessively subtile are the walls of the onidce, that 

 it was not until after many observations that I detected 

 them ; in an example from T. orassicornis, which had 

 discharged about half of the wire, I have not seen the 

 slightest sign of armature on the ecthoroBwm. So far as 

 my investigations go, these Spiral Cnidse are confined 

 to the walls of the tentacles, in which, however, they 

 are the dominant form." 



Such, then, is the form and armature of these 

 organs. But I have not yet done with them. The 

 emission of the wire, strange to say, is a process of 

 distinct eversion from beginning to end. The ecthm^CBUTn 

 is not a solid, but a tubular, prolongation of the walls 

 of the cnida, turned-in, during its primal condition, like 

 the finger of a glove drawn into the cavity. Of this 

 fact you may convince yourself by a careful watching 

 of the phenomena before you. Many of the eothorcBa 

 from the tangled cnida, now under your eye run out, 

 not in a direct line, but in a spiral direction. Select 

 one of these, and you will perceive that each bend of 

 the spire is made, and stereotyped, so to speak, in suc- 

 cession, while the tips go on lengthening ; the tip only 

 progresses, the whole of the portion actually dischai'ged 

 remaining perfectly fixed ; which could not be on any 

 other supposition than that of evolution. 



In the discharge of the chambered kind — to revert 

 to those which we were just now examining — we saw 



