6 HISTORY OF THE HUMAN BODY 



of Protozoa, and while in the present state of knowledge it 

 cannot be asserted that it is a universal procedure, existing in 

 all species, it is very likely that this or a similar process is oc- 



FIG. 3. Conjugation. Diagrams based on the infusorian Paramacium. 

 Here the two gametes are of the same size and the fusion is temporary 

 with similar results in the case of each. 



(a) The two micronuclei are forming mitotic figures preparatory to division, 

 (b) The two micronuclei have elongated; the macronuclei are disintegrating. (c) 

 One-half of each micronucleus passes into the other individual through the 

 mouth, (d) Fusion occurs in each individual between the half nucleus 

 that originally belonged to it and the half nucleus that has come from 

 the other. This forms a fusion-nucleus, (e) The fusion-nuclei form mitotic figures 

 preparatory to division. At about this time the two individuals separate. (f), (g), 

 (h) The fusion-nucleus divides three times in succession, eventually forming eight 

 nuclei. (i) Four of the eight nuclei enlarge and form macronuclei, and four re- 

 main small and become micronuclei. These become associated in pairs, one micro- 

 and one macro-nucleus, and are distributed to four individuals that result from 

 two successive divisions. Each of these, evidently as the result of the conjugation, 

 has a renewed power of fission, and multiplication continues in this way [cf. Fig. i] 

 until the power becomes diminished, when it is renewed by a new conjugation 

 [cf. Fig. 5 (a)]. 



casionally undergone in all cases. This is the process of con- 

 jugation [Fig. 3] which, in the cases best studied, seems to 

 bear a definite relation to the process of reproduction by 

 fission. In these cases the number of fissions which can occur 

 in succession appears to be limited, for after a series of these 



