182 WHEEL-BEARING ANIMALCULES. 



The rotifera are oviparous ; they produce eggs, 

 from which the young are excluded, sometimes 

 while yet within the body of the parent. The eggs 

 of some of these animalcules, appearing like minute 

 transparent globules, are calculated to be, when 

 first deposited, only the twelve thousandth part of 

 an inch in diameter ; but they increase in magni- 

 tude, and then constitute most interesting objects of 

 microscopic examination. In an egg of about the 

 one thousand and seven hundredth part of an inch in 

 diameter, the included animalcule may be distinctly 

 perceived, even the actions of the cilia may be dis- 

 tinguished, producing the wheel-like rotatory ap- 

 pearance previously described. At certain times, 

 the eggs may be easily recognised before being 

 deposited by the animalcule, lodged in a long float- 

 ing sac, in the cavity of the body ; for the trans- 

 parency of the creature is such as to permit the 

 minutest parts of its internal structure to be seen ; 

 but it often happens that the sac is empty. 



Such, then, is the general outline of what we 

 know of the structure of the rotifera. They are 

 active and vivacious creatures, and by the celerity 

 and address of their movements, give delight to 

 those who observe them. To see a shoal of them 

 in a drop of water, avoiding each other in their 

 mazy courses, and performing a thousand mingled 

 evolutions, is perhaps one of the most interesting 

 spectacles which the reflective can contemplate ; 

 but this delight gives way to astonishment, or 



