ANIMAL NATURE OF DIATOMEiE. 353 



morphological facts which appear manifest in the more 

 simple organisms, are repeated in the more corapKcated ; 

 that the primitive organic structure is very similar in the 

 two kingdoms ; in short, that in the first instance every 

 plant, every animal, and every tissue in the one or the 

 other, proceeds solely from cells. And since the primi- 

 tive state, which in superior beings is only transitory, 

 remains permanent in the inferior, we have thus, as well 

 in planis as in animals, very' simple beings, reduced 

 indeed to the simplicity of a single cell. We do not 

 here inquire whether we have viscera, systems, tissues, on 

 the one hand, or roots, leaves, flowers, or even fronds or 

 spores, on the other ; the difference we are endeavouring 

 to determine is in the primitive cell, that cell which 

 represents the ovum or the spore as transitory beings, or 

 the Protococcus and the Gregarina as permanent beings. 

 The field is open, and its boundaries are well defined. 

 The vegetable cell on one part, and the animal cell on 

 the other, but both alike in their first origin, in their 

 formation, in every successive change. 



If a dangerous rock present itself here, and if we 

 cannot steer entirely clear of it, we ought at least to 

 point it out in order to prevent shipwreck. The means 

 by which we endeavour to augment the power of our 

 senses have a limit. The microscope reveals the presence 

 of a corpuscle only the iOO,OOOth of a millimetre in 

 size ; yet, since this corpuscle may be large in comparison 

 with those which entirely elude our vision, can we ever 

 boast that we are able to perceive the internal structure 

 even of larger bodies flian this ? Hence there is always 

 great danger of believing that to be simple which in 

 reality only seems to be so, and which the wonderful 

 artifice of organisation may conceal from our eyes by its 

 transparency, or by the compact nature of its parts. 

 Since the impossibility of penetrating deeper into struc- 

 ture is inherent in the means we resort to for the purpose, 

 we may still avail ourselves of comparison as a guide, 

 deducing nothing from observation beyond what is com- 



23 



