MEMOIRES. li 



performs as is well known many very active movements. 

 Take another example from amongst the simpler forms 

 of life, — cryptogamic plants, whose spores, possessing 

 contractile filaments, hâve considérable powers of exten- 

 sion and contraction, and are otherwise employed as 

 motile agents. We may then without further argument 

 assume, that Diatoms are furnished with a somewhat 

 similar agencv, whereby their movements are effected, 

 We hâve diversity ofform, structure and means employed 

 to ensure the same end, but it has been observed, that 

 there is nevertheless a « reign of law » throughout ail 

 Nature 's opérations and works. 



Somewhat conclusive évidence of the préhensile con- 

 tractile filamentous theory, is, I believed, furnished by 

 the addition of a minute quantity of colouring matter to 

 the contents of the cell, in which the Diatoms are con- 

 fined.When a particle or two of colouring matter cornes 

 within reach of a filament, it is seized upon, and follows 

 the subséquent movements of the Diatom. 



Oceasionally a coloured particle will be seen to bc 

 affected in the following manner. At a point equal to the 

 length of the frustule, it is grasped en passant ; or it may 

 be seized at some intermediary distance of the extrême 

 lirait of the préhensile filament, when it is instantly 

 drawn towards the frustule with a jerky motion, and 

 secured. On more than one occasion, a cell of Palmo- 

 glœa was seized in the way described, and seen to 

 travel along the longitudinal suturai aspect of the valve, 

 and in a contrary direction to that of progression, the 

 progress of the frustule being at the moment percept- 

 ibly slower and somewhat more jerky. When not so 

 engaged it appeared to be occupied in securing points 



