SEA-ANEMONES AND THEIR ALLIES. 79 



The third and last class of the Coelentera includes a few 

 beautiful free-living forms to be found floating at the surface 

 of the sea. They may occasionally occur in the rock pools, 

 but are more likely to be found in the open water, where 

 they may be seen as little iridescent bells floating past the 

 boat, in company with the tiny swimming-bells and the giant 

 jelly-fish. These iridescent globes of jelly are members of 

 the class CTENOPHORA, and differ markedly both from the 

 true jelly-fish and from the swimming-bells. Two genera 

 are not uncommon, Beroe and Pleurobrachia (see Fig. 93), 

 sometimes called "iridescent fire-globes," or "sea-gooseberries." 

 In the former the body is oval in shape with a wide mouth 

 occupying the whole of the under surface, in the latter it is 

 somewhat pear-shaped with a small mouth. When removed 

 from the water both are colourless and delicately transparent, 

 but when seen in active movement in the water both gleam 

 with rainbow tints. This is due to the fact that the long 

 axis of the body, from pole to pole, is traversed by eight 

 bands of motile plates (four of these are shown in the figure), 

 which in life are in constant movement, and propel the 

 animal through the water, while by breaking up the light 

 they also produce the changing play of colour. The structure 

 of the body in both JSeroe and Pleurobrachia is a little 

 complicated, so we need only notice further that the latter, 

 but not the former, has two very long delicate tentacles 

 which can be instantly retracted, or allowed to stream out 

 like a long train behind the body (see Fig. 93). Both are 

 most delicately beautiful animals in life, and should be 

 looked for every summer, if only for the sake of their play 

 of colours and graceful movements. As in the jelly-fish, 

 most of the charm is lost after death. 



Perhaps it may be thought that in this and the preceding 

 chapter we have eulogised ad nauseam the delicate beauty 

 of a group of animals known to most people chiefly as 

 "nasty stinging jelly-fish," but it is difficult to tear one's self 

 away from a group whose members are adapted for so many 

 different kinds of surroundings, and yet are essentially so 

 simple and so uniform in structure. Their fascination, too, 

 is enhanced by association, for many of them are "fair- 

 weather animals," and all must be studied in the open air 

 for their beauty to be fully appreciated. To anyone who 



