NATURE'S JEWELS. 161 



seat of life, and of all the wonderful functions of 

 which the whole Diatom is the agent. Although 

 the Diatoms vary greatly in form, the structure 

 here indicated is common to all. In some forms 

 there is an additional external investment, consisting 

 of a mucous or gelatinous substance, and in which 

 they lie imbedded, side by side or end to end, in 

 filaments or chains of various patterns ; or they 

 are attached by their angles in a zig-zag manner ; 

 or aggregating in masses, they build up a fairy tree- 

 like or frondose form, or group in irregular bosses 

 around the stems of plants. Although the Diatom 

 exhibits these social tendencies in a greater or less 

 degree throughout its vast species, yet each one is 

 perfectly distinct in all that pertains to its own in- 

 dividual life, and in the majority the association is 

 only that of free companionship with its fellows. 



The especial importance of the girdling zones 

 is only fully seen in connection with the propaga- 

 tion or re -production of the Diatom. Self -division 

 is the common method here, as it is also with all 

 the humble forms of life and for that matter of 

 all the higher and more complex beings, whether 

 of animal or vegetable nature the only difference 

 L 



