42 HETEROMITA less. 



The zygote remains quiescent for some time, j^nd then, 

 after undergoing wave-like movements of its surface, bursts 

 at its three angles (e'''), 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 

 (f^) are found to grow into clear visibility and to take on a 

 distinctly oval shape {y''-\ Still increasing in size they 

 develop a ventral flagellum (f^) which is at first quite 

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

 becomes an anterior flagellum (f^). The spore has now 

 become a Heteromita resembling the parent form in all but 

 size. As growth proceeds a nucleus becomes apparent. 

 All analogy leads us to believe that this is not a new 

 structure, but that the multiple fission of the protoplasm of 

 the zygote is preceded by the multiple fission of its nucleus, 

 each spore having thus its own ultra-microscopic nucleus 

 from the very first. 



It will be seen that this mode of multiplication following 

 conjugation differs from ordinary multiplication by fission in 

 that it requires the co-operation of two individuals which 

 undergo complete fusion. As we shall see more plainly 

 later on (Lessons XV., XVI.) conjugation leads to the 

 simplest case of sexual reproduction, differing from the sexual 

 reproduction of the higher organisms in that the two conjugat- 

 ing 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,^ but 

 each takes an equal and similar share in the production of 



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



