Reproduction and Life-Cycles 67 



degree from the extranuclear spindle of Pseudotrichouymplia and similar 

 types (Fig. 2. 10, I, J). Comparable extranuclear spindles occur in certain 

 dinoflagellates (29, 195) and in Aggregata (20). Since the nuclear mem- 

 brane persists in such forms as Pseudotrichonympha, some of the astral 

 rays, during development of the spindle, make connections with the cen- 

 tromeres at the nuclear membrane. Each chromosome in HoJomastigo- 

 t aides (Fig. 2. 10, H), for example, ends in a terminal centromere which 

 remains anchored to the nuclear membrane. Duplication of the centro- 

 mere parallels that of the chromonema. In some of the Hypermastigida, 

 development of the spindle and its connections with the chromosomes has 

 been followed in living flagellates. Pulls exerted on the achromatic figure 



D 



Fig. 2. 9. Mitosis in the ciliatc, CoDchophthirius auodontae; x3995 

 (after Kidder). A. Longitudinal splitting of the chromosomes. B, C. Sepa- 

 ration of daughter chromosomes. D. Nuclear division nearly completed. 



cause corresponding movements of the chromosomes; when the tension 

 is released, the fibrils and chromosomes snap back into place (59). 



Intranuclear figures have been described in the micronuclei of ciliates, 

 in Actinophrys (IS), Monocystis (184), ^nd Euglyph a (120), among others 

 (Fig. 2. 11, E-L). In some of these cases, the spindle ends in centrosomes 

 which seem to be embedded in the nuclear membrane or else adherent to 

 it. An intranuclear spindle is typical of the dividing micronucleus (Fig. 

 2. 11, E, F), although little is known about division-centers in ciliates. 

 The spindle sometimes extends into achromatic masses ("polar caps") 

 which may or may not contain "centrioles." Only a granule has been 

 described at each pole in certain ciliates, and even the granules seem to 

 be missing in others. 



