CONJUGATION 79 



This complicated process is best comprehended by reference to the diagram 

 (Fig. 43). Except for variations in detail, the conjugation of other ciliates 

 in which the process has been studied takes place in a similar manner. In 

 Paramecium 'putrinurn the two conjugants are equal in size. In other 

 ciliates a large individual conjugates with a smaller one, while the most 

 extreme condition is reached in Vorticella and its allies, in which a small 

 free-swimming ciliate budded of! from a large pedunculate individual 

 conjugates with one of the large forms (Fig. 44). The macronuclei in both 

 degenerate, and the micronuclei undergo a number of divisions, as in 

 Paramecium. All these degenerate except one which divides to give rise 

 to a stationary and a migratory nucleus. Each individual, one a large 

 and the other a small one, now contains two nuclei. Exchange of nuclei 

 then occurs, as in Paramecium, but the small individual, instead of pro- 

 ceeding to further development, shrinks and dies, while the large individual 

 alone survives. The single nucleus of the large surviving individual divides 

 repeatedly, and a number of macronuclei and one micronucleus are 

 produced. By successive divisions of the ciliate, similar to those occurring 

 in Paramecium 'putrinutn, the original condition is regained. In the case 

 of Paramecium caudatum, the process of syngamy is similar to that of 

 P. putrinutn (Fig. 45), but in the case of P. aurelia, owing to the fact that 

 the ciliate possesses two micronuclei instead of one, it is modified in certain 

 respects. When conjugation occurs, the two micronuclei of each conjugant 

 divide twice, so that eight are formed. Of these seven degenerate, leaving 

 in each conjugant one micronucleus and one degenerating macronucleus. 

 The single micronucleus divides and exchange of nuclei occurs, as in P. jnitri- 

 num and P. caudatum. After union of the two nuclei the single nucleus 

 divides twice till four are present, and of these two become macronuclei 

 and two remain as micronuclei. Each of the latter divides once, so that in 

 each ciliate there are now two macronuclei and four micronuclei. The ciliate 



A. Union of the small free-swimming conjugant with the large attached one. 



B. Fragmentation of the macronuclei and division of the micronuclei. 



C. D. E. Further divisions of the micronuclei leading to four in the large conjugant and eight 



in the small one. 



F. All the daughter micronuclei have degenerated except one in each conjugant. 



G. The two micronuclei are dividing with the axis of division across the plane of union of the two 



conjugants. 

 H. The two micronuclei in the large conjugant are uniting, while those in the small one remain 



separate. 

 I. The two micronuclei m the large conjugant have united, while those in the small one are 



degenerating. 

 J. The micronucleus of the large conjugant is dividing, while the small conjugant is shrinkmg. 

 K. The small conjugant has disappeared, while the micronuclei of the large one are dividing. 

 L, 31. Further divisions of the micronuclei to give rise to eight. 



X. Transformation of seven micronuclei into macronuclei and division of remaining micronucleus. 

 0, P. Division of the body has taken place, giving rise to an individual with four macronuclei 



and one micronucleus (O), and one with three macronuclei and one micronucleus (P). By 



further divisions the original condition is reached in which the micronucleus and one macro - 



nucleus are present. 



