MISCELLANEOUS PAPERS. 385 



fellows with mouths, and excrete them, so as to dissolve solid food 

 which may have been captured by his flagellum. This is the condi- 

 tion of our mouthless mastigophore. He digests and absorbs just 

 enough solid food, we may believe, to serve as a proper stimulus to 

 get more ; and this stimulus, we may imagine, led some ancient mas- 

 tigophora to form solid spheres, the morul?e, or hollow spheres, the 

 blastulse, or double-walled cups, the gastrulse. Fairly good examples 

 of these we find in the eudorina and pandorina, which stop develop- 

 ment at the solid sphere and then begin conscious activity ; in the 

 volvox, which develops till it becomes a hollow sphere and then takes 

 upon itself full conscious activity; and in the fresh-water hydra, 

 which develops from the fertilized egg, passing through the morula 

 and blastula stages and reaches the gastrula stage, where it takes to 

 itself all the conscious activities of an independent organism. 



If it is hard to believe that these simple organisms may form hab- 

 its, be subconsciously active, and have these modes of activity finally 

 established as instincts, we should recall some of the wonderful things 

 learned about the bacteria, those tiny, one-celled plants which divide 

 and subdivide so as to form new generations every few hours, and are 

 much simpler in many ways than the mastigophora and yet much 

 like them in being provided with flagella. 



It has long been known that, among the pathogenic bacteria, the 

 same species may at one time be exceedingly virulent, and, at other 

 times, be mild and even almost innocuous. 



It has lately been discovered that the nitrogen-fixing bacteria bury 

 their instincts beneath new habits with the greatest ease. Doctor 

 Nobbe, an eminent German bacteriologist, conceived that it would be 

 possible to make a fortune selling nitrogen-fixing bacteria to the 

 farmers, so he prepared cultures of these bacteria to sell at a dollar a 

 bottle. Doctor Nobbe's "nitragin," as he called it, was worthless, for 

 he had so satiated the bacteria with rich, nitrogenous foods that they 

 had lost their desire and, indeed, their ability, to use free nitrogen. 

 It remained for an American, Dr. Geo. T. Moore, to discover this fact 

 and to devise a way by which our department of agriculture could 

 supply to the American farmer, at a cost of only a few cents a cake, 

 nitrogen-fixing bacteria that are so hungry for atmospheric nitrogen 

 that they are doubly efficient. 



Of higher mold than the hydra, the mammalian embryo does not 

 stop at the gastrula stage of growth, but, by cell multiplication and 

 differentiation and a series of secondary and tertiary invaginations and 

 a few evaginations, it next develops the tissues, organs and cavities 

 which characterize the adult animal. To the time of independence 

 of the mother, these activities are all instinctively performed ; but 

 -^25 



