Conjugation in Didinium Nasutum 179 



Figure 47. Reduction of the number of chromosomes, and other 

 processes in the nuclei, at conjugation in Didinium nasutum. After 

 Prandtl, 1906. 



A and B, the first of the three divisions of the micronuclei ("first 

 maturation division"). In A, a spindle has been formed with 16 chromo- 

 somes; in B, each chromosome has divided, so that two groups of 16 

 are present; one group to go to each of the two resulting micronuclei. 



C, D, E and F, the second division (the "reducing" division). C, 16 

 chromosomes; spindle forming for division. D, the 16 chromosomes 

 beginning to separate into 2 groups. E, the 16 chromosomes have sep- 

 arated into 2 groups of eight each, each going to one of the two result- 

 ing micronuclei. F, the two resulting micronuclei, each with 8 chromo- 

 somes; still united by a connecting strand from the spindle. 



G, H and I, the third division, which forms from a single nucleus 

 the migratory and the stationary nucleus. G, each of the 8 chromosomes 

 dividing. H, the two groups of 8 chromosomes widely separated, to 

 pass into the two resulting nuclei. I, the migratory nucleus (above) 

 and the stationary nucleus (below) still joined by a connecting strand. 

 The stationary nucleus already considerably larger than the migratory 

 nucleus. 



J, the migratory nucleus passing through the membrane that sep- 

 arates the two mated animals, into the other individual. 



K, union of the migratory and the stationary nuclei. The latter 

 (above) is much larger than the former. L, the two nuclei almost 

 completely united. 



M, the first division of the nucleus formed by the union of the migra- 

 tory and stationary nuclei. The union is not quite complete, so that 

 at the right end two spindles can be seen. Each of the 16 chromosomes 

 has divided into two, so that two groups of 16 are now present. 



