54 SMITHSONIAN MISCELLANEOUS COLLECTIONS [voL. 48 
smaller individuals must be formed at each repetition of this process, 
as the two new valves are always formed within the old ones. The 
diatom loses approximately one-sixtieth of its length by this method ; 
and if it were continued indefinitely the forms would necessarily 
dwindle to the vanishing point! This however is corrected by means 
of the second or sexual method of reproduction, a process that brings 
about two important results ; the diatom’s vitality is rejuvenated and 
its ancestral size is restored. This process, called conjugation, may 
take place in any one of three ways ; — 
1. The nucleus of a single diatom divides karyokinetically; the 
cell contents swell, bursting apart the valves; the mass passes out 
into the water, becomes spherical, secretes a large quantity of jelly- 
like substance; the two daughter nuclei reunite; a large “auxo- 
spore” is formed, and within this a single large diatom is built, like 
the parent frustule, but approximately double the size. See Figs. 12 
and 13. 
2. The second method is where two diatoms come into contact; 
the contents swell, as before; the two nuclei remain undivided, but 
fuse together and produce a single auxospore, within which a single 
diatom, double the former size, is again formed. See Fig. 14. 
3. In the third method two parent diatoms join; the nucleus of 
each divides karyokinetically; the four daughter nuclei unite, the 
two from one plant with the two from the other, producing two 
auxospores and giving rise to two large frustules. See Fig. 15. 
The first method is common among diatoms that are fixed, and 
especially those which grow in long filaments. The second is 
