180 Life and Death, Heredity and Evolution 



have 16 chromosomes, until another reduction occurs 

 preparatory to another mating. 



In the infusorian Anoplophrya branchiarum, which is a 

 parasite in the blood of the fresh water crustacean Gam- 

 marus, the number of chromosomes is 6. These are reduced 

 to 3 before the mating (Figure 48) ; by the union of two 

 at mating the number 6 is restored (Collin, 1909). 



In Opercularia coarctata, a relative of Vorticella, accord- 

 ing to Enriques (1907), the unreduced number is 16; the 



Figure 48. Conjugation and reduction in the number of chromosomes 

 in the infusorian Anoplophrya branchiarum, after Collin, 1909. A, 

 the two micronuclei (after the first maturation division) have each 6 

 small chromosomes. B, each micronucleus dividing anew, showing the 

 separation of the group of 6 into two groups of 3, one at each end 

 of the spindle. 



reduced number 8. The reduction occurs at the second of 

 the three maturation divisions; and the number 16 is re- 

 stored at mating. In the infusorian Chilodon uncinatus, 

 according to the same author (Enriques, 1908), the number 

 of chromosomes before reduction is 4. At the second 

 maturation division, these are reduced to 2, in the usual way. 

 Mating restores the original number 4. 



In Carchesium, according to Popoff (1908), the micro- 

 nuclei have, before the time of mating, 16 chromosomes. 

 At the first maturation division 8 of these go into one of the 

 resulting half nuclei, 8 into the other. At the second and 

 third divisions each of these 8 chromosomes divides into two, 



