116 



The Microscope. 



indicate the readiness with which their component 

 parts separate. They were set down as animals by 

 the eminent Professor Ehrenberg, but are now classed 

 as plants by a number of careful investigators. 



The " little wedges on branched stems," No. 13 

 in my list, are also diatoms, by 

 name Gomphonema geminatum. 



The diatoms might in strictness 

 be excluded from a chapter on ani- 

 malcules; still as some naturalists 

 continue to class and describe them 

 as animals, some notice of them may 

 be considered admissible ; especially 

 as many examples of the tribe, when 

 dried and mounted on slides are 

 well-known microscopic objects of 

 extraordinary beauty ; and the 

 reader may look at these with added 

 interest, after comparing them with 

 these humbler specimens found in 

 a living state. 



A great variety of form occurs 

 in the different species of diatoms. In the Diatomavul- 

 qare, represented above, which gives its name to the 

 whole group, its component cells are oblong, and gene- 

 rally in a state of partial separation, being joined by a 

 gelatinous hinge at the corners. Sometimes, how- 

 ever, two or more cells may be seen side by side, as 

 in the third link from the right in the figure. Other 

 diatoms, besides this one, have the same curious 

 arrangement for joining at their corners ; two of these, 



No. 14. Diatoma 

 vulgare. 



