m CONJUGATION 275 



certain peculiarities. A Vorticella divides either into 

 two unequal ha-lves (F 2 ) or into two equal halves, one of 

 which divides again into from two to eight daughter- 

 cells (F 1 ). There are thus produced from one to eight 

 microzooids which resemble the barrel-shaped form (E 3 ) 

 in all but size, and like it become detached and swim 

 freely by means of a basal circlet of cilia. After swim- 

 ming about for a time, one of these microzooids comes 

 in contact with an ordinary form or megazooid, when it 

 attaches itself to it near the proximal end (G 1 ), and 

 undergoes gradual absorption (G 2 ), the mega- and 

 micro-zooids becoming completely and permanently 

 fused to form a zygote (p. 251). 



Notice that in this case the conjugating bodies or 

 gametes are not of equal size and similar character ; 

 but one which is conveniently distinguished as the 

 microgamete (= microzooid) is relatively small and active, 

 while the other or megagamete ( megazooid, or ordinary 

 individual) is relatively large and passive. As we have 

 seen in the case of the frog (pp. 195 and 196), this 

 differentiation of the gametes is precisely what we get 

 in the higher animals, and, in fact, in almost all organ- 

 isms with two sexes : the microgamete being the 

 male, the megagamete the female conjugating body 

 (p. 197). 



The result of conjugation is somewhat different in the 

 two cases just studied : in Paramoecium no zygote is 

 formed, conjugation being a mere temporary union 

 (p. 268) : in Vorticella the zygote is an actively moving 

 and feeding body, indistinguishable from an ordinary 

 individual of the species. 



Vorticella sometimes encysts itself (Fig. 72, H 1 ), and 

 the nucleus of the encysted cell has been observed to 

 break up into a number of separate masses, each doubt- 

 less surrounded by a layer of protoplasm. After a time 



