32 NATURAL HISTORY 



he has not, however, demonstrated the form of their 

 alimentary structure. 



4. BoDO didynms.—Size, l-9600th to l-1440th of an 

 inch. 



5. vorticellaris. The whirling Bodo, — 1- 1200th 



of an inch in diameter. 



6. viridis. The green Bodo. — 1 -6000th of an inch. 



7- MoNAS guttula, E. new species. The drop Monad. — 



This animalcule is larger than the atom monad, and 

 somewhat globular. On account of its size and trans- 

 parency, its digestive cavities can be much more dis- 

 tinctly observed. It revolves about its longer axis, and 

 in swimming, that part which contains the coloured 

 particles follows the colourless part. Occasionally, with 

 attentive observation, currents in the water may be seen 

 about the fore-part or mouth ; it is therefore highly pro- 

 bable that it is furnished with ciliae or hairs. Those 

 found at Petersburgh measured from l-3000th to l-2300th 

 of an inch in diameter : they are represented in the en- 

 graving, Group 4, magnified 380 times. 



8. MoNAs mica. The grain Monad. — The digestive or- 

 gans of this animalcule have not as yet been observed. 

 According to Muller, it is a monad surrounded by a circle. 

 It does not require so deep a power as any of the pre- 

 ceding, and is capable of elongating itself from a glo- 

 bular to an oval figure at pleasure. It is transparent, 

 and, according to Baker, has a small ellipse inscribed, 

 as it were, within its circumference. This ellipse is move- 



