SEA-ANEMONES : THEIR WEAPONS. 871 



I detected them; in an example from T. crassicornis, 

 which had discharged about half of the wire, I have not 

 seen the slightest sign of armature on the ecthoreum. So 

 far as my investigations go, these Spiral Cnidse are con- 

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

 are the dominant form.* 



Such, then, are the form and armour of these organs. 

 But I have not yet done with them. The emission of the 

 wire, strange to say, is a process of distinct evolution, or 

 expansion from within, from beginning to end. The ectho- 

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

 walls of the cnida, turned-in, in its first condition, like 

 the finger of a glove drawn inwards. Of this fact you 

 may convince yourself by a careful watching of the phe- 

 nomena before you. Many of the ecthorea 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 succession, while the tips go 

 on lengthening ; the tip alone progresses, the whole of the 

 portion actually discharged 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 the 

 ventricose basal part first appear; the lower barbs flew 

 out before the upper ones, and all were fully expanded 

 before the attenuated portion began to lengthen. This, 

 again, is consistent only with the fact of the evolution of 

 the whole. On several occasions of observation on the 

 chambered cnida of C. Smiihii, I have actually seen the 

 unevolved portion of the ecthoreum running out through 

 the centre of the evolved ventricose portion. But per- 

 haps the most instructive and convincing example of all 



♦These details, with many others, are given in my Hist, of Brit. 

 Sea-anemones and Corah, Introd., xxii — xl. 

 B B 2 



