A STATISTICAL STUDY OF MITOSIS AND AMITOSIS. 245 



This is what I have tried to do in the case of Fasciolaria, and 

 what seems to me ought to be done in other forms. Merely 

 stating that mitosis and amitosis occur, without also stating how 

 frequently, does not meet the requirements of the problem. 



If his interpretation of the life history of Amoeba proteus is cor- 

 rect Calkins ('07) has advanced an absolutely conclusive case in 

 which direct nuclear division is a link in a normal life-cycle. 

 Calkins believes he has found evidence adequate to show that in 

 Amceba proteus an asexual period is succeeded by a sexual 

 one inaugurated by amitotic multiplication of the nucleus. The 

 "primary nuclei" thus formed fragment and change to minute 

 granular " secondary nuclei." The secondary nuclei later con- 

 jugate giving rise to the "fertilization nuclei" ; "in these the 

 fused karyosomes fragment to form finely divided chromatin 

 (it is strictly speaking, not a chromidium for it is entirely intra- 

 nuclear), while a vacuole forms in the interior ; this vacuolated 

 fertilization nucleus becomes a center of multiplication (equivalent 

 in every way to a sporozoon sporoblast) ; by accumulation of 

 these fine chromatin granules the peripheral or ' tertiary ' nuclei 

 are formed ; the tertiary nuclei, surrounded by a minute bit of 

 plasm, grow into the pseudopodiospores observed by Scheel 

 (hypothetical) ; these young pseudopodiospores break away from 

 the parent cyst and develop into young amoebae fromerly known 

 as Amceba radiosa, and these in turn develop into the ordinary 

 Amoeba proteus of pond and laboratory." If this represents 

 truthfully the life cycle of Amceba, we have at least one conclu- 

 sive case in which amitosis cannot be ruled out, for here there 

 are no mitoses. Neither are there any degenerating cells to cast 

 their shadow of suspicion on the other cells. Equally conclusive 

 cases can hardly be hoped for among the higher animals, although 

 what seems to be true for Amoeba, may be also true of multicel- 

 lular forms. If it proves impossible to establish these facts with 

 mind-compelling certainty, further investigation should be able at 

 least to endow them with a degree of probability amounting to a 

 practical demonstration. 



Summary. 



1. During the period of cannibalism, the entoderm of Fasci- 

 olaria becomes first spindle-shaped, but later as regional differ- 

 entiation occurs, the cells become cuboidal. 



