REPRODUCTION 197 



Boell and Woodruff (1941) noticed that in P. calkinsi, living indi- 

 viduals of one mating type will agglutinate with dead ones of the 

 complementary mating type. A similar phenomenon was also ob- 

 served by Metz (194(5, 1947, 1948) who employed various methods of 

 killing the animals. The pairs composed of living and formaldehyde- 

 killed animals, behave much like normal conjugating pairs; there is 

 of course no cross-fertilization, but the living member of the pair 

 undergoes autogamy. While the "mating type substances" can be 

 destroyed by exposure to 52°C. for five minutes; by X-irradiation; 

 by exposure of formaldehyde-killed reactive animals to specific anti- 

 sera or to 100°C, etc., Metz demonstrated that animals may be 

 killed by many reagents which do not destroy these substances. 

 Furthermore, all mating activities disappear when the animals are 

 thoroughly broken up, which suggests that Paramecium might re- 

 lease some mating substance inhibitory agent. This agent was later 

 found in this Paramecium (Metz and Butterfield, 1950). Metz (4948) 

 points out that the mating reaction involves substances present on 

 the surfaces of the cilia, and supposes that the interaction between 

 two mating-type substances initiates a chain of reactions leading up 

 to the process of conjugation and autogamy. Hiwatashi (1949a, 

 1950) using four groups (each composed of two mating types) of P. 

 caudatum, confirmed Metz's observation. Metz and Butterfield 

 (1951) more recently report that non-proteolytic enzymes (lecithin- 

 ase, hyaluronidase, lysozyme, ptyalin, ribonuclease) have no de- 

 tectable effect on the mating reactivity of P. calkinsi; but proteo- 

 lytic enzymes such as trypsin and chymotrypsin destroy the mating 

 reactivity, and mating substance activity was not found in the digest 

 of enzyme-treated organisms. The two observers believe that the 

 mating reactivity is dependent upon protein integrity. 



When the ciliate possesses more than one micronucleus, the 

 first division ordinarily occurs in all and the second may or may 

 not take place in all, varying apparently even among individuals 

 of the same species. This seems to be the case with the majority, al- 

 though more than one micronucleus may divide for the third time to 

 produce several pronuclei, for example, two in Euplotes patella, Sty- 

 lonychia pustulata; two to three in Oxytricha fallax and two to four in 

 Uroleptus mobilis. This third division is often characterized by long 

 extended nuclear membrane stretched between the division prod- 

 ucts. 



Ordinarily the individuals which undergo conjugation appear to 

 be morphologically similar to those that are engaged in the trophic 

 activity, but in some species, the organism divides just prior to 



