232 



ROTIFERA. 



paddle-wheels, carry it rapidly along with an equable 

 gliding movement. 



Some of these little creatures are enclosed in a trans- 

 parent shell, often variously armed with spines at one 

 or both extremities, but others are not so enclosed. 



The eggs of the Rotifera form beautiful objects 

 for microscopic study. They are covered with a 

 transparent shell, through which the parts of the 

 embryo, as they develop themselves, gradually be- 

 come distinctly apparent, until at length the cilia 

 are seen performing their mimic rotation, though as 

 yet the imprisoning shell has not been broken. At 

 last, by the action of these organs, which every 

 moment becomes more energetic, the transparent 

 membrane is ruptured, and the little creature bursts 



forth, eager to enter 

 <*W% upon its new existence, 

 >^t>yj and already possessing 

 rthe form of its parent. 

 The time from the ex- 

 clusion of the egg to the 

 hatching is commonly 

 about twelve hours. 

 Ehrenberg watched an in- 

 dividual through eighteen 

 successive days ; it was 

 full grown when he first 

 observed it, and it did 

 not die of old age at last. 

 Such an individual he 

 found to be capable of 

 producing four eggs every 

 twenty-four hours, the 

 progeny derived from 

 which grow to maturity 

 and exclude their fertile 

 ova in the same period, a 

 single Rotifer thus pro- 

 ducing in ten days forty 

 eggs, developed with the rapidity thus stated ; this 



FlG. 178. BKACIUOSUS. 



