DIATOMACE^!. 307 



many observations, which fully confirm us in the view we 

 then took of their motile power ; with this slight difference, 

 that cilia do not appear to be constant ; and that the act of 

 progression as performed by some, rather favours the idea 

 of contractile tentacular filaments pseudopodia being 

 the organs both of locomotion and prehension with them. 

 These filamentous organs are of so delicate a nature, that, 

 as yet, no power of the microscope has enabled us, posi- 

 tively, to make out their forms and attachment. Some 

 deny the presence of a membranaceous hyaline covering, 

 which we have certainly seen; the defining power used, 

 and mode of illumination, is at fault; consequently, they 

 cannot see what we do; but this constitutes no valid 

 argument against the existence of cilia. Professor W. 

 Smith admits the existence of a structureless membra- 

 naceous covering, at some periods of growth, in many of 

 the Diatomacece, but he denies the existence of a ciliated 

 or other motile power, save that occasioned by "exos- 

 motic and endosmotic forces." 



Dr. Carpenter says : " It is a question whether this be 

 anything else than an optical illusion, arising from the 

 existence of currents at these orifices, produced by the 

 vital actions going on within the cell." Both of the 

 views above propounded, appear to us difficult of com- 

 prehension, and are far from satisfactory explanations 

 of a simple motive power, found almost universally 

 effected by the agency of cilia. Why then jump to the 

 conclusion, that this motion is " endosmotic force " ? How 

 is it possible to prove such an assumption 1 Certainly not 

 by the aid of microscopy, or its sister science chemistry. 

 The same question may be put to the supporters of the 

 vital force theory. "What is it? where situated 2 how pro- 

 duced? and so forth. Aristotle, centuries ago, showed 

 that sensibility especially characterises animal life. He 

 says : " That creatures endowed with sensibility are not 

 merely living beings, but animals, although they may 

 neither be motive nor change their locality. Touch is the 

 sense first manifested in all creatures, and, as the nutritive 

 faculty can bo manifested independently of Touch and 

 other senses, so the sense of T.ouch can be manifested 

 independently of anv other. We call nutritive function 

 x2 



