II] PARAMEC1UM 41 



forth when a specimen first touches the drop it is forced back and 

 turned to one side and when it resumes its normal state it will 

 probably pass by the side of the obstacle. Thus the behaviour of 

 Paramecium is almost as simple as that of a Jack-in-the-box. 

 Other Ciliata such as Vorticella are a little more complex in their 

 behaviour; they may have two or even three reactions, but in none 

 is there any question of intelligence. 



If a single Paramecium be introduced into a sterile food solution 

 it will grow and rapidly multiply, and if when the solution is used up 

 a single individual of the brood be transferred to another solution the 

 race may be kept going through hundreds of generations. Such a 

 race all sprung from a single individual is termed a pure culture. 

 After some hundreds of generations the members of a pure race 

 attempt to conjugate with one another, but nothing results. Soon 

 after they exhibit signs of degeneration, imperfect individuals with- 

 out mouths result from fission and the whole race perishes in the 

 midst of plenty of food. This catastrophe can be staved off by 

 adding stimulating substances to the solution (Calkins) but cannot 

 be finally averted. If however members of a different culture are 

 introduced successful conjugation takes place and the vitality of 

 the culture is renewed. When such a conjugation is about to take 

 place two individuals approach and place their oral surfaces in 

 contact, the mouths and gullets of both disappear and their proto- 

 plasm fuses. The meganucleus breaks up into pieces which are 

 absorbed. The micronucleus in each divides into eight nuclei and 

 of these seven are absorbed the remaining piece divides into two 

 and one of these migrates into the other animal and fuses with the 

 resting half of its micronucleus forming thus a zygote nucleus. Thus 

 it may be said that each animal gives off a single male gamete to 

 the other and is itself the female gamete. The animals then separate 

 and each forms a new mouth and pharynx. The zygote nucleus then 

 divides into eight nuclei, four of which enlarge to form new mega- 

 nuclei. Then the animal divides into two, each daughter having two 

 micronuclei and two meganuclei ; then after a day or two it divides 

 again and now the cycle is complete, each daughter having one 

 meganucleus and one micronucleus. The whole process of conjuga- 

 tion has for its result the installation of a new meganucleus and 

 the idea is suggested to the mind that in the processes of ordinary 

 division and growth during which the meganucleus must be giving 

 off substances into the protoplasm, it becomes worn out in its 

 essential parts and must be replaced, and this can only happen if 

 nuclear matter from another source, which if worn out is probably 



