606 



MARCUS M. HARTOG. 



" It is obvious/' says Maupas, " that this division, unprovoked 

 by any nuclear division, must be due to the forces of the pro- 

 toplasm, the nuclear elements only playing a passive part." 



MiM 



(1st fission). 



H 



Z2 



Z2 7? 



Z* 



Fig. 2. — Reconstitution of nuclear apparatus from conjugation-nucleus in an 

 exconjugate ColpidiumColpoda, and reversion by a single fission to the 

 normal type with single mega- and micro-nucleus (M, m). The dotted 

 vertical line indicates the plane of fission. 



We may express this by equations thus : 



Z = 4 Z^ (Stages F, G). 



4Z2 = 



= 2 M -f 2 m (Stage H). 



= {M + m} -f {M-j-m} (1st fission). 



The original meganucleus is passive throughout, and retains 

 its granular structure till Hg. At H3 it becomes homogeneous, 

 and still stains well ; while in H^ it passes to the hinder end 

 of the body, becomes smaller and irregular, loses its staining 

 power, and finally disappears completely. The above dia- 

 grams (Figs. 1, 2) are modified from Maupas. 



We may sum up matters thus : — In each gamete the micro- 

 nucleus undergoes three bipartitions ; two sister nuclei of the 

 third bipartition are diflPerentiated into stationary or female 

 pronucleus, and migratory or male pronucleus respectively. 

 By fusion of a male and female pronucleus a copulation-nucleus 

 is produced ; by two successive mitoses are formed four 

 nuclei of the formula Z^ ; the sister nuclei of either pair are 

 differentiated in their development to form the one a mega-, 



