18971 MICROSCOPICAL JOURNAL. 35 



al80 that the (Mitire epidermal coat may be actively en- 

 gaged in gathering up any character of minute mineral 

 or other debris along its path. Such [)articles as become 

 attached, are independently moved from numerous cen- 

 ters of vital action. This is as if the epidermal surface 

 at any given point had a retractile and contractile [)Owe]', 

 independent of any other given ])oint of vital action along 

 the frustuhir surface. The motile functions consist of 

 the power of transporting small mineral particles such 

 as sand grains and vegetal debris for appreciable dis- 

 tances along its edges or surface, and of rejecting then] 

 and substituting new particles. The particles may be 

 jerked up at any point and carried indifferently in a posi- 

 tive or negative direction from the point of attachment, 

 until these particles are replaced by new ones. It should 

 strike any observer who may verify these phases of ac- 

 tion that such plienomena point to a more Ci)mplex cilia- 

 like function tlian that which may be noted in the ciliary 

 fi-inges of an oyster or clam. The latter cilia motion 

 lashes and drives the particles in a general direction or 

 current. The complicated system of moving particles 

 can also be followed in its interminable variations as long 

 as it may suit the convenien(;e of the observer to change 

 the specimen of Nitzschia under observation, on account 

 of its relatively conspicuous size. Nitzschia scalaris is a 

 very satisfactery species in which to study the character 

 of its vital movements. 



The internal frustular contents present an abundance 

 of globular bodies of varying sizes which have a constant 

 independent motion among themselves, that is, their juxta- 

 position is seen to be constantly changing when very 

 carefully noted. 



Nitzschia scalaris when viewed under a power of 500 

 di'i meters is longer than any other of the North Ameri- 

 can specimens of the bacillar forms, and therefore can be 



