II CONJUGATION 279 



thus produced from one to eight microzooids which resemble 

 the barrel-shaped form (e') in all but size, and like it become 

 detached and swim freely by means of a basal circlet of cilia. 

 After swimming 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 (g1), and under- 

 goes gradual absorption (g^), the mega- and microzooids 

 becoming completely and permanently fused to form a 

 zygote (t^ 197). As in Paramoecium, conjugation is followed 

 by increased activity in feeding and dividing. 



Notice that in this case the conjugating bodies or gametes 

 are not of equal size and similar characters ; but one, which 

 is conveniently distinguished as the niicrogamete ( = micro- 

 zooid) is relatively small and active, while the other or 

 megagamete (= megazooid, or ordinary individual) is rela- 

 tively 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 organisms with two sexes : the 

 microgamete being the male, the megagamete the female 

 conjugating body (see p. 197). 



The result of conjugation is somewhat different in the two 

 cases already 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^), and the 

 nucleus of the encysted cell has been observed to break up 

 into a number of separate masses, each doubtless surrounded 

 by a layer of protoplasm. After a time the cyst bursts, and 

 a number of small bodies or spores (h^) emerge from it, each 

 containing one of the products of division of the nucleus. 



