SPONGES AND CORALS 



having cell-bodies provided with whip-like tails — are 

 extremely complicated in structure and exhibit a vast 

 range of designs, often singularly beautiful. Every con- 

 ceivable pattern appears among them — circular shapes, 

 oval ones, elongated forms, and others — numbers of them 

 having radial and other designs which rival those of 

 stained-glass windows. 



Methods of feeding are variable. Food may be taken 

 in at well-defined spots, sometimes but not necessarily 

 oral, or it may be absorbed in solution through the 

 general surface of the body. 



The body structure is apparently simple in most cases, 

 but this only makes the movements of the flagella more 

 mysterious. Among the free-swimming flagellates we 

 have enormous swarms of living creatures which, like the 

 thread-slime, have no brains or nervous systems, yet 

 control their activities as though they possessed either or 

 both ; have no stomachs, yet can digest their food ; have 

 no true eyes, yet can move about and direct themselves as 

 though they can see ; and have no sexual systems yet can 

 reproduce themselves prolifically and perfectly. 



Many spermatozoids and free-swimming algae cells 

 have been observed moving at speeds which (considering 

 their microscopic size) are comparatively far greater than 

 any speeds attainable by humans using cars or aircraft. 

 One species of the ciliated protozoa, using its flagella to 

 attain the speed, has been scientifically timed at two 

 thousand microns per second — nearly six inches a 

 minute. Comparing the relative size of the creature with 

 the distance, man would need to travel at thousands of 

 miles a minute to attain comparable speeds. 



Realizing that the flagella and the cilia are so 

 similar in their structures and characteristics that it is 

 impossible to classify them separately, the wide range 

 of their activities can be generally listed. They run right 

 through the plant kingdom from single-celled algae and 

 mosses and ferns; through the animal kingdom from 



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