THK NATIRK OF DIATOM MOTION. I25 



quence, the spennato/.oids go along into the egg cell with the 

 same vigor exhibited by the boy climbing the tree. But 

 merely to label the phenomenon "positive chemotaxis " is 

 not to explain the motion of the spermatozoid. The malic 

 acid did not set the spermatozoid in motion. It was already 

 going. A cloud of spermatozoids will be going in all possible 

 directions. The acid of the tgg cell merely makes it pleasant 

 for the spermatozoid to swim in one special direction rather 

 than in any and every direction. Meantime each and every 

 spermatozoid has started forth with a certain small store of 

 energy-producing material, starch or some other cary:)ohydrate 

 or hydrocarbon or the like, and is drawing upon this endow- 

 ment every moment of its brief career, converting it in effect 

 into water and carbon dioxide as it goes ; until at last, in case 

 no delicious stream of malic acid guides it to its proper place, 

 it dies of exhaustion. The striving, agonizing piece of pro- 

 toplasm has used up its food upon the quest and has worked 

 itself to death. So far is motion in the fern spermatozoid 

 from being explained by the operation of any force outside 

 itself. 



There is no radical difference between this case and that of 

 the diatom. Both belong to the wrestling race of living 

 things ; both wrestle, and both expend stored-up energy in 

 the process. Both need oxygen and both exhale carbon 

 dioxide as they go. Details differ, since the diatom cell man- 

 ufactures its own store of food, and stows it away in the 

 shape of drops of an oil soluble in ether, while the sperma- 

 tozoid's has been furnished for it by its mother plant. I^ut no 

 matter about details. The man eats bread and meat. It is 

 the same in 'principle all the way along, from man to diatom, 

 and so down to the Annrba. 



As to mechanism, that is a subject of itself, and one set 

 round with difficulties. 



