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half fused finally separate, one, or ÌDoth, or neither immediately encysting 

 by throwing of the cilia and generally part of the protoplasm and form- 

 ing a very delicate cyst (fig. 7). In a few cases encystment of the same 

 sort followed complete fusion. It is not usual and I beleive that when it 

 occurs it is abnormal. (Neresheimer describes encystment as normal.) 

 Observation of the nuclear phenomena of conjugation is still continuing. 

 When the macrogamete has one nucleus it fuses obliquely, end to end 

 with the nucleus received from the microgamete, I have once in the 

 living animals seen the nucleus of the microgamete enter and fuse with 

 the posterior nucleus of a binucleated macrogamete, and I have had 

 acetic carmine preparations which indicate the fusion of the nucleus 



Fiof. 4. 



Fio-. 6. 



Fio-. 7. 



Fig. 4. Conjugation in Opalina caudata. Fusion of the gametes has gone a httle 

 further than in the case shown in fig. 3. Observe the three chromosomes in each 

 nucleus, also the spherules in the endosarc and ectosarc. Near the nucleus of the 

 microgamete is a vacuole which in the drawing appears like a spherule of the ecto- 

 sarc. From an acetic-carmine preparation. The cilia and the spherules of the ectosarc 

 were omitted in the original sketch and have been supplied by comparison with other 



preparations. X 620 diameters. 

 Fig. 5. A zygote of Opalina intestinalis in which the nuclei from the macrogamete 

 are both in a late stage of mitosis, -while the nucleus from the microgamete is not 

 yet in division. The rays at the ends of the spindle-shaped microgamete nucleus are 

 merely threads of the general cytoplasmic reticulum. Their resemblance to astral 

 rays is deceptive. The body of the zygote is beginning to divide. From an acetic 



acid preparation in which the cilia were injured. X 620 diameters. 

 Fig. 6. A macrogamete of Opalina intestinalis with two nuclei each containing four 

 masses of chromatin, indicating the probable presence of four chromosomes in each 

 nucleus. Nuclei of macrogametes of this species when in mitosis show clearly four 



chromosomes. From an acetic-carmine preparation. X 620 diameters. 

 Fig. 7. A macrogamete of Opalina intestinalis with the nucleus in mitosis (four 

 daughter chromosomes in each end). This gamete was found in an early stage of 

 conjugation (cf. fig. 3). Later it separated from the microgamete, which at once threw 

 off its cilia and became spherical. Ten minutes later the macrogamete also became 

 spherical and threw off its cilia and part of its cytoplasm, as shown in the figure. This 

 pseudoencystment I think is pathologic. X 620 diameters. 



