BRITISH ZOOPHYTES. 143 



3. Spiral cnidge, in which the edJioreum is a long, 

 cylindrical thread, coiled into a close and regular spiral. 

 (See Plate XL fig. 5 a.) 



The threads are tubular, and are believed to be ejected 

 from the cnidae by the expansion under irritation of 

 the fluid contained in the cnidee, which expels the 

 threads with very considerable force. How the threads 

 act so as to inflict fatal wounds upon the minute 

 organisms into which they enter is not properly known. 

 Mr, Gosse considers that the ecthorea are filled with 

 some poisonous fluid which pours out through openings 

 in the barbs, and enters the tissues of the animal 

 attacked, the everted form of the barbs preventing the 

 withdrawal of the ecthoreum when once inserted. 



The British anemones belonging to the sub-order 

 Sclerodermata deposit a corallum or internal calcareous 

 skeleton. The parts of the corallum are the base and 

 wall, the latter sometimes ribbed, the plates formed 

 in the septa, the palules, which are arranged in a circle 

 or circles between the septal plates and the centre, and 

 the columella, which is a series of twisted plates at the 

 bottom of the cavity. The plates, like the septa, are 

 arranged in cycles. The hollow centre of the coral 

 above the plates is called the calyx. 



There are three modes of reproduction amongst the 

 anemones — fission, gemmation, and sexual generation. 

 Fission occurs either by longitudinal splitting or by 

 the chipping off, as it were, of parts of the base, each 

 part becoming a complete animal. 



Gemmation principally occurs in those genera which 

 possess a corallum or stony skeleton. It, however, 

 occurs in other genera very largely, the buds appearing 

 sometimes on the disc and at others on the base. 



