OF MICR O- OR GANISMS. 65 



does not bring about the same movement that a body 

 situated at the left does; a particle of the nutritive 

 sort does not provoke the same course of action that 

 a particle of a different sort does. All this implies 

 that associations have been established in the proto- 

 plasm between certain excitations and certain move- 

 ments. The explanation of the physical nature of 

 these association appears to us totally impossible. 



The quite ingenious ideas broached by Spencer 

 upon the lines of least'resistance offered by the com- 

 misural fibres cannot be applied here, since everything 

 takes place in a single cell. What would be necessary 

 to explain is how and in consequence of what mechan- 

 ism of structure one form of molecular movement, cor- 

 responding to a given excitation, is followed by a cer- 

 tain other form of molecular movement correspond- 

 ing to an act likewise determined. 



VI. 



FECUNDATION. 



We now enter upon a subject fraught with obscu- 

 rity. We shall limit our investigations to ciliated In- 

 fusoria, as it is among these species that fecundation 

 and the psychical phenomena attendant thereon have 

 been best observed. 



Ehrenberg had established by his authority the pre- 

 vailing opinion in science "that copulation never takes 

 place among Infusoria, and that all facts observed by 

 early writers as connected therewith are to be re- 

 garded as phenomena of longitudinal fissiparity. This 

 erroneous idea prevailed unquestioned until 1858, 

 when M. Balbiani addressed a communication to the 

 Academy of Sciences, wherein he showed that sexual 



