ALG.E. 173 



that writers such as Meneghini, who contended for 

 the animal nature of the Diatomaceae, quaHfied it by 

 the supposition "that in a being whose nature, for 

 other reasons, we beHeve to be animal, the move- 

 ments may be effected by the admirable vital powers 

 through organs which escape our sight by their 

 minuteness." 



In a letter from M. Petit, quoted by Montagne,^ 

 he says, " The motion of these Naviculcs is well worth 

 attention. It is more or less decided according to 

 the degree of their development. In their more or 

 less rapid progress across the field of view, they 

 appear to have a certain degree of consciousness, so 

 as to avoid any obstacles with which they meet. 

 They advance for the purpose of investigation ; they 

 try the obstacle with one of their extremities: but they 

 appear to do this with a certain degree of precaution. 

 It seems as though they smell at these obstacles, 

 that they examine them, and try means of avoiding 

 them. I may add that I am quite certain that the 

 movements of these little creatures do not depend 

 on currents arising from the evaporation of the fluid 

 on the stage, or from any other physical cause, of 

 which it is easy, with a little attention, to convince 

 one's self. These movements are certainly self- 

 dependent, for the creatures wander in different, and 

 frequently opposite, directions ; and they consist, not 

 simply in an agitation without object, but seem to 

 be directed by a sort of instinct. On carefully 

 watching them, we see them turn round obstacles 



• Montagne, " Sylloge Crypt.," p. 471 (1856). Annals lYat, IIL^t. 

 (1856), xvii. p. 278. 



