42 HETEROMITA LESS. 



The zygote remains quiescent for some time, and then, after 

 undergoing wave-like movements of its surface, bursts at its 

 three angles (E G ), its contents escaping in the form of granules 

 called spores, so minute as to be barely visible even under 

 the highest powers of the best modern microscopes. They 

 are formed by the protoplasm, of the zygote dividing into an 

 immense number of separate masses, a process known as 

 multiple fission. 



Carefully watched, these almost ultra-microscopic particles 

 (p 1 ) are found to grow into clear visibility and to take on a 

 distinctly oval shape (r 2 ). Still increasing in size they 

 develop a ventral flagellum (r 3 ) which is at first quite 

 quiescent : finally, the pointed end sends out a process which 

 becomes an anterior flagellum (r 4 ). The spore has now 

 become a Heteromita resembling the parent form in all but 

 size. 



It will be seen that this remarkable mode of multiplication 

 by conjugation differs from multiplication by fission in the 

 fact that it requires the co-operation of two individuals which 

 undergo complete fusion. As we shall see more plainly 

 later on (Lessons XV. and XVI.) conjugation is the simplest 

 case of sexual reproduction, differing from the sexual repro- 

 duction of the higher organisms in that the two conjugating 

 bodies or gametes are each an entire individual, and in the 

 further circumstance that the gametes resemble one another 

 in form and size, so that there is no distinction of sex, 1 but 

 each takes an equal and similar share in the production of 

 the zygote. Binary fission, on the other hand, is an example 

 of asexual reproduction. 



1 It might perhaps be allowable to consider the active, free- 

 swimming monad which seeks and attaches itself to the anchored form 

 as a male, and the passive anchored form as a female gamete 

 (see Lesson XII.). 



