OF MICRO-ORGANISMS. 71 



The material changes effected inside the bodies of 

 Infusoria in copulation do not extend to all their or- 

 gans; the main mass of the body, the protoplasm, plays 

 but a secondary role in the matter; the change appears 

 to be effected exclusively in the nucleus and the nu- 

 cleole. 



Let us further state that, so far as is known, these 

 changes are never effected apart from coition and be- 

 fore the Infusoria actually embrace; copulation sets 

 in every time, apparently, that these animals, under 

 particularly favorable conditions, have actively repro- 

 duced by fission. Fissiparity is then seen to cease 

 and conjugation appears. 



We have not the time to sketch the history of this 

 important question of physiology, interesting as it may 

 be. It will be enough to recapitulate what we actu- 

 ally know upon the subject, taking as our guide sub- 

 stantially the views of M. Balbiani who, as is known, 

 was the first scientist to study the physical phenome- 

 na connected with fecundation among Infusoria. The 

 divergencies between his observations and those of an- 

 other eminent investigator, M. Biitschli, extend in re- 

 ality only to points of detail. 



Let us first mark the modifications that take place 

 within the Chilodon cucullus during conjugation. Each 

 of the two Infusoria in copulation possesses a nucleus 

 (endoplast, main nucleus) and, close beside this nu- 

 cleus, an organ considerably smaller, a nucleole, or 

 attendant nucleus, or latent nucleus (endoplastule, 

 accessory nucleus); this minute body must not be mis- 

 taken for the nucleole that is often found in the inte- 

 rior of the nucleus among many Micro-organisms and 

 in cellules; it has a function entirely different. 



Of these two elements, the nucleus plays an al- 



