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 



