14 Dr. G. C. Wallich on the Diatomacea. 



discuss the statement of Professor Ehrenberg as to his haying 

 seen " moveable retractile cirrhi," on a species of Surirella, bear- 

 ing a resemblance to " the feet of the sea-stars/' by which loco- 

 motion was effected. 



As it is, I would observe that, having repeatedly seen the pecur 

 liar appendages described by Professor Ehrenberg and recognized 

 by Professor Smith, I have shared the inability of the last-named 

 high authority to distinguish the slightest evidence of motile 

 power. Prof. Smith states that he never saw the appendages 

 move. In so far as relates to their being deflected, one after 

 the other, during the transit of the frustule to which they were 

 attached past impeding objects, I have certainly seen move- 

 ments ; but these movements were precisely of a character to 

 furnish the most conclusive proofs against their being organs of 

 locomotion, or indeed anything more than epiphytic appendages 

 which, like the teeth of a comb, when drawn across an object, 

 become the exponents and not the source of the force employed. 



Before proceeding further, I must avow that, whilst I am 

 prepared to indicate the kind of organs possessed by the Diato- 

 macese, I have hitherto failed in rendering them visible under 

 the microscope, even with all the delicate appliances of an 

 instrument of the most perfect construction. 



In. venturing to prove my position, I rely on two facts : viz. 

 that the hypothesis offered is sufficient to account for the entire 

 series of phenomena, and that the phenomena observed are 

 wholly irreconcileable with any other hypothesis. 



Under this difficulty, I may perhaps be permitted to record, 

 in the first place, the several conditions under which the living 

 Diatom may be seen to move and to exert an influence upon 

 minute particles in its course ; and then to point out the nature 

 of the organs by which alone I conceive those conditions can be 

 effected*. 



The normal motion of the Diatomaceous frustule is in two 

 opposite directions, which accord with its longest diameter. It 

 is of a smooth, gliding nature, devoid of jerks or interruptions, 

 and exhibits itself at tolerably regular intervals. The rate at 

 which it travels is not uniform, being subject to variation on 

 increase or diminution of light and warmth. The rate is also 

 materially influenced by the condition of the endochrome, the 

 motions being invariably more active and energetic when the 

 frustule is full. On the other hand, as soon as the contents 

 shrink, and more especially on the appearance of vibratile 



* The appearances about to be described may be readily seen in any of 

 the commoner Naviculoid species. If kept in saucers for a day or two, 

 they will rise to the surface, in a sufficiently pure state to admit of accu- 

 rate observation. 



