8 



HISTORY OF THE HUMAN BODY 



FIG. 4. Carchesium, a sessile protozoan colony, showing conjugation. 

 [Diagram in part after BUTSCHLI and SCHEWIAKOFF.] 



a a Macrozooids, which, by their division produce either b, other macrozooids, or 

 c microzooids, which eventually become free, d Free-swimming microzooids, per- 

 haps from another colony, d microzooid (here a microgamete) in conjugation with 

 a macrozooid (macrogamete). In each of the above individuals may be seen a 

 vermiform marcronucleus and a spherical micronucleus. e Detail of conjugation. 

 The macronucleus of each component is shown broken into fragments previous to dis- 

 solution; the two micronuclei are dividing mitotically into two halves, one-half of each 

 destined to pass into the other component. The micro- and macro-gametes are 

 designated, respectively, as male and female. [Subsequent stages similar to those 

 shown in Fig. 3.] 



