678 GARY N. CALKINS 



toiy of the 'capsules.' The first statement, liowever, in i"ej>;anl 

 to the unchangeableness of the macronucleus cannot hold for 

 B. undulans. On the contrary, this is the very center of nuclear 

 activity, and its early changes initiate the internal processes 

 of conjugation. These early changes are characterized mor- 

 phologically by three conditions of the macronucleus, not pres- 

 ent at other times: (1) all macronuclear material is concen- 

 trated in one definite oval macronucleus; (2) this oval nucleus 

 is enclosed in a thick doubly refractive cyst-like membrane; 

 (3) the cleft or Kernspalt which appears occasionally in the 

 vegetative nucleus, is here continued into a clear hyaline space 

 which separates the nuclear material into two distinct parts. 



The material of the macronucleus at this stage is condensed 

 into a firm, massive nucleus with a characteristic appearance 

 quite different from its appearance at other periods. The 

 cyst-like membrane has not the least resemblance to nuclear 

 membranes as usually seen. It has a distinct double contour 

 and is separated by a clear space from the chromatin contents, 

 and if seen free from the surrounding cell, would give to the 

 macronucleus the appearance of an encysted flagellate (fig. 12). 



The early changes of the micronuclei have not been seen, 

 that is, their emergence from the macronucleus. Until fusion 

 is completed they remain comparatively small and difficult 

 to see, showing no such enlargement as do the micronuclei of 

 Paramecium or other ciliates in which conjugation has been 

 worked out, and staining with the greatest difficulty. In rest- 

 ing cells the characteristic number appears to be four. In 

 conjugating cells there is often, but not always, a fifth micro- 

 nucleus-like body which takes no part in the processes accom- 

 panying conjugation (figs. 12, 18 and 20). It degenerates and 

 ultimately disappears. It may be an extra vegetative micro- 

 nucleus, since the number of these nuclei varies in the vegeta- 

 tive cells; or it may be a residual degenerating nucleus from a 

 first maturation division of the four nuclei, an interpretation 

 which would bring the maturation phenomena of Blepharisma 

 in accord with the phenomena in other ciliates. On this inter- 

 pretation there would be three other similar nuclei to account 



