92 NATURAL HISTORY 



The mouth is situated in the concavity marked by the 

 dotted line and cross. The tissue which envelopes the 

 animalcule is transparent and colourless^ covering all 

 the integuments of the body except at the lower ex- 

 tremity. Its digestive organs are polygastric, con- 

 sisting of numerous spherical cavities or sacs, branch- 

 ing out from the alimentary tube ; these are capable of 

 great dilatation, which is rendered peculiarly manifest 

 after it has swallowed a Navicula ulna, as shewn in the 

 drawing. They are very persevering in search of their 

 prey, examining every thing within their reach in the 

 most scrutinizing manner. They creep along, and swim 

 in the manner shewn by the group of young ones attached 

 to two pieces of confervae, figure 86. At other times, 

 when their food is floating in the water, they remain 

 stationary, and create a current towards them by the 

 cilia, as in figure 85. 



For the increase and continuance of the species, the 

 parent animalcule is separated, either vertically, longi- 

 tudinally, or obliquely. These different modes of propa- 

 gation seem to be indeterminate, it having never been 

 ascertained whether the longitudinal, vertical, or other 

 division, are the result of particular circumstances. To 

 afford the reader an idea of their appearance while under- 

 going division, I have given two figures from Ehrenberg, 

 which, like the others, are magnified 380 times. The 

 first, figure 88, exhibits an animalcule undergoing a 

 transverse section ; and figure 87? another about to be 

 divided longitudinally. They are found in various in- 



