344 SYDNEY J. HICKSON. 



are not convincing. In none of these papers are the stages 

 of the enlargement of the micronnclear element to form the 

 characteristic meganuclear body very complete^ and it seemed 

 to me that there was just a possibility that these authorities 

 were mistaken^ and that the new meganucleus arises indepen- 

 dently in the cytoplasm^ or from one or more of the old 

 meganuclear fragments. This hesitation in accepting the 

 orthodox view was due to the fact^ that in the earliest stages 

 I had then found of the formation of the new meganucleus 

 there was no chromatin in its centre. It was, moreovei% very 

 much larger than any of the other micronuclei, and the con- 

 nection between it and a micronucleus could not be traced. 



The subsequent discovery of the intermediate stages, how- 

 ever, removed my doubts, and now I feel that it is quite an 

 established fact that the new meganucleus is formed from 

 one of the four nuclei produced by the second division of the 

 germ nucleus. Plate, Schneider, and Sand, who maintain 

 that the new meganucleus is formed by the reconstitntion of 

 one or more fragments of the old meganucleus, are in error, 

 and I believe that the views expressed by Maupas and 

 Hertwig as to the origin of the new meganucleus in Ciliata 

 are correct. 



The principal stages in the formation of the new mega- 

 nucleus are shown in PI. 18, figs. 2 — 5. In the first stage 

 one of the four micronuclei (figs. 1 and 2) increases in size in 

 a manner very similar to that in which the micronuclei swell 

 up just before mitosis in bud formation, or in the earlier 

 stages of conjugation. In the preparation, the enlarged 

 micronucleus was 5 ju in diameter, and the others 4 ju. This 

 enlargement is caused by a considerable increase in the clear 

 substance, and by the resolution of the chromatin into a 

 coarse skein. In the next stage (fig. 3) the nucleus has still 

 further increased in size to about 8 /i in diameter; the 

 chromatin has become more diffused, and does not stain so 

 deeply. It is probable that the change in staining power 

 indicates some slight change in constitution, but there is 

 no evidence as to the natui-e of this change. The greater 



