Law of Proenvironment 225 



Therefore the writer would suggest here, as before, that it 

 might appropriately be called the cognitonucleus. The micro- 

 nucleus may lie against or be considerably removed from the 

 mega- or cognitonucleus. When conjugation of two individuals 

 has been effected "the micronucleus of each swells up and 

 undergoes division by mitosis into two micronuclei. This is 

 immediately followed by a di\'ision into four. Of these four 

 nuclei three degenerate, and are either absorbed or ejected 

 from the body. The remaining one, which behaves as a sexual 

 nucleus, undergoes division into two nuclei. One of these 

 crosses the line of junction of the two conjugating indiidduals, 

 and enters the cytoplasm of the other individual, and may be 

 called the migratory nucleus. The other remains in the cyto- 

 plasm of the parent, and may be called the stationary nucleus. 

 Thus, as a result of the divisions of the original micronucleus 

 of each of the conjugating individuals, five nuclei are formed: 

 three degenerate and disappear, one migrates, and the re- 

 maining one is stationary. A fusion of the migratory nucleus 

 of one individual and the stationary nucleus of the other then 

 takes place to form the cleavage nucleus, and soon after this 

 has occurred the two individuals separate. The cleavage 

 nucleus then divides into two, and generally a second time 

 into four, or a third time into eight. Ultimately, however, 

 one of the halves of a division gives rise to the new meganucleus, 

 and the other to the micronucleus of a new individual. The 

 new meganucleus can therefore be traced back to its origin 

 from micronuclear elements, and to this there is no excep- 

 tion." (5^:389.) 



Here then the micronucleus behaves as a special hereditary 

 or sexual or reproductive nucleus. It would, further, be of 

 extreme interest to ascertain whether fine connections do not 

 exist between the mega- or the micronucleus and the peripheral 

 ectoplasm, which usually is highly sensitive and even differ- 

 entiated into two or more layers. Of these, one, kno^m as 

 the neuroneme layer, has been regarded as nervous in function, 

 and, if derived from or connected with the meganucleus or 

 micronucleus, might well be homologized with the ectoplasmic 

 cogitonucleus of the Hcernoflagellata. But, even in want of 

 such recognizable nuclear demonstrations, it can be accepted 

 that a cogitonuclear, a cognitonuclear, and a hereditary sub- 

 stance are all segregated in some Infusoria. 



These epitomized studies then definitely suggest that, in two 

 of the highest groups of Protozoa, four specializations in cell- 

 substance have been effected, viz., the protoplasm or sub- 



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