12 THE LOWEST FORMS 



to which angular grains of sand are adherent. This has been 

 secreted, or rather excreted by the surface portion of the animal, 

 and the minute fragments of sand are stuck on by some un- 

 known process. At one side of the sac there is an aperture, 

 through which alone the body can protrude. This is not to 

 be seen in the figure, because it is on the opposite side of the 

 shell to that which is here represented. From this aperture 

 the body sends out processes (b) similar to those of Amoeba; 

 but they appear to have a more definite character, and a 

 seemingly more especial office than in that animal. These pro- 

 cesses have been called pseudopodia^ i. e. false feet, by which 

 name 1 shall designate them hereafter. Owing to their ex- 

 ceeding transparency, the pseudopodia, as they stretch out 

 over the surface upon which the animal creeps, remind one 

 of water spreading in streaks over glass, and sending off little 

 branches, here and there, sideways. Sometimes only a single 

 pseudopod is stretched out, and waves gently from side to side 

 as if feeling for something. 



One cannot help but admire the caution with which this 

 seems to be done, for after reconnoitering awhile the other 

 pseudopodia come forth. There would seem to be good rea- 

 son to believe that the animal really does exercise at least an 

 instinctive caution, from the timidity which becomes apparent 

 when it is disturbed ; for instantly, and as if with a sudden jump, 

 the body darts toward the ends of the pseudopodia, and the latter 

 being contracted in the act, are then drawn into the shell. The 

 leap thus made is owing to the fact that the contraction of the 

 pseudopodia is more rapid than the loosening of their hold, and 

 consequently they drag the whole body toward the point of at- 

 tachment. 



I mention this phenomenon particularly that I may draw your 

 attention to the rapidity of the muscular contraction which is ex- 

 hibited in the act. We are apt to suppose that a low degree of 

 organization has a correspondingly low vitality ; and this is true 

 to a certain extent; but we are not justified in supposing it to 

 be in exact parallelism with the organic grade of the animal, for 



