224 



THE PROTOZOA 



tilization, or of so-called sexual reproduction, throughout both animal 

 and vegetable kingdoms. 



3. The union of swarm-spores (Isogamy and Anisogamy). 



It is but a short step from the primitive condition described above, 

 where an ordinary individual unites with a smaller one, to the condi- 

 tion where both conjugants are reduced — indeed, both conditions may 

 be present in the same organism. Thus the genus Polytoma, as de- 

 scribed above, shows a facultative union between two normal-sized 

 individuals, or between one normal-sized individual and a microgamete, 

 or between similar microgametes. Other members of the group to 



which Polytoma be- 

 longs — the Chlamy- 

 domonadina — show 

 similar indefinite- 

 ness, and in no case 

 can it be positively 

 stated that the union 

 between a larger 

 ( ovoid) and a smaller 

 (spermatoid) micro- 

 gamete is obliga- 

 tory. Goroschankin 

 ('75) maintained that 

 in Cklorogonium pul- 

 visculus the sperma-- 

 toid microgametes 

 arise by an eight 

 division and con- 

 jugate with the 

 ovoid macrogametes 

 which arise by a two 

 or four division (Fig. 

 .123), but Reinhardt 

 ('76), on the other 

 hand, observed conjugation between microgametes of the smaller size, 

 although he noted a frequent difference in size. ' In Polytoma, while 

 there is a facultative conjugation between individuals of diverse size, 

 there is also, apparently, a tendency toward an obligatory union of 

 microgametes. The differentiation goes a step further in Phacotns 

 lenticularis, where, according to Carter ('58), an ovoid cell arising by 

 two or four division in the normal manner, unites with a minute form 

 which is the product of a sixty-four division. 



The obligatory conjugation of microgametes is, however, safely 



- Eplstylis umbellaria Leeuw. 

 [Greeff.] 

 Macrogametes {M) and microgametes {m). 



