SPONGES AND CORALS 



covered with mucus, possess flagella which *'wave" the 

 egg-cells onwards and downwards, so that they may be 

 fertilized by the spermatozoa, which ascend towards 

 them by using their own flagella — their whip-like tails. 

 Neither the larger egg-cells of the female, nor the tadpole- 

 like spermatozoa, of the male, could manage their ex- 

 traordinary journeys unaided, although the spermatozoa 

 have a kind of semi-independent motion as they oscillate 

 their flagella : they both need the propulsive help of the 

 waving ''whips" which line the female Fallopian tube. 



Whether we consider them as devices, plants or 

 animals — and all three terms are applicable — we are 

 compelled to believe that flagellates are baffling and 

 mysterious, in all their diversified forms, from those 

 which create the light in the water (wrongly described 

 as "phosphorescent") when disturbed in their myriads 

 by the passing of a steamer, to those which may break 

 away from a human throat, be ejected in mucus, and 

 swim for some time (Hke living protozoa in the sea, with 

 independent life and action) within that discharged 

 mucus. 



We have apparently travelled a long way from the 

 sponge, but it is here a case of the longest way round 

 being the shortest way home. For no appreciation of the 

 real nature of a sponge's flagella would be possible with- 

 out some idea of the enormous diversity of cilia and 

 flagella in the animal and vegetable kingdoms. 



Sponges in millions occur in the world's coral reefs. 

 Others thrive in areas where there are no corals. Some 

 sponges are non-aggressive: others are almost ferocious 

 as they bore their way into solid rock. All sponges have 

 their flagella, linking them with plants and animals and 

 with man himself in curious relationships which indicate 

 the underlying unity of all living creatures. 



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