in COELENTERATA 45 



On the free margins of the partition walls 



R6 tion U g astl> i c filaments are developed, recalling the gastric 



filaments in a Scyphozoan (see p. 39) ; these 



probably secrete a digestive juice ; also the generative organs, 



either egg cells or sperms, develop on these septa (see Fig. 20, e). 



The sexes are nearly always distinct, though a few rare 



hermaphrodite anemones are known (e.g. Cerianthus). 



The fertilised eggs usually undergo a certain amount of 

 development inside the parent anemone, forming a little 

 jelly-like ciliated larva which escapes through the mouth of 

 the parent and lives a free-swimming life for a time, before 

 settling down in one place and assuming the adult form. 

 Stinging The stinging cells are abundant on the tentacles 



Cells. and also on the outer surface of the body- wall ; 

 in some Sea-anemones they are grouped together in little 

 batteries of cells, which may form conspicuously bright- 

 coloured beads round the margin of the mouth-disc, at the 

 bases of the outer tentacles, as in the Common Beadlet 

 (Actinia mesembryanthemum) which is very common on our 

 coasts. This is a form with many tentacles, and with a body 

 very variable in colour, but usually of a deep red, with bright- 

 blue spots round the disc, and a line of bright blue round 

 the base of the column. The dart cells in this species are not 

 sufficiently strong to pierce human skin, but their ejection 

 when touched causes the tentacles to adhere slightly, pro- 

 ducing a peculiar sticky feeling. 



In other genera there are special defensive organs in the 

 shape of long threads covered with the stinging dart cells ; 

 these threads arise on the internal vertical septa, but they 

 can be projected through holes in the body-wall, and then 

 drawn in again ; they are known as acontia. 



Corals. 



Devon Cup In nearly all our British Anthozoa, the polyp 

 Coral. consists of a soft or leathery body with no 

 supportive skeleton, but a few, such as the Devon Cup 

 Coral (Caryopliyllia smithii), form calcareous matter within 

 the body-wall, and the calcareous particles become fused 

 together, attaching the anemone firmly to the rock on which 



