INHERITANCE 



753 



and with the inheritance of size (De Gads, 1935) . That on mating type 

 will be presented first. 



INHERITANCE OF MATING TYPE IN Paramecium aurelia 



In Paramecium aurelia, according to the work of Sonneborn (1937, 

 1938, 1939), there are in any variety but two mating types, members of 

 which unite in conjugation as the two sexes unite in multicellular ani- 



Figure 175. The four clones (al, a2, bl, b2) produced from the two ex-conjugants 

 (a and b) of a pair, in the experiments of Sonneborn and of Jennings. 



mals. Three varieties or "groups" are known; individuals of one variety 

 do not conjugate with individuals of the other varieties. 



In Variety or Group 1, the two mating types are known as types I 

 and II. These unite in conjugation. In studying the types produced by 

 them, each ex-conjugant after separation was allowed to divide once, and 

 from each of the products a clone was produced by vegetative reproduc- 

 tion. Thus four clones were derived from each pair, two from each ex- 

 conjugant, as shown in Figure 175. 



