226 



FERTILIZATION OF THE OVUM 



times successively, and of the eight resulting bodies four become 

 macronuclei and four micronuclei (Fig. no, H-K}. By two suc- 

 ceeding fissions the four macronuclei are then distributed, one to each 

 of the four resulting individuals. In some other species the micro- 

 nuclei are equally distributed in like manner, but in P. caudatum the 

 process is more complicated, since three of them degenerate, and 

 the fourth divides twice to produce four new micronuclei. In either 

 case at the close of the process each of the conjugating individuals 



B 



D 



Fig. in. Conjugation of Vorticellids. [MAUPAS.] 



A. Attachment of the small free-swimming microgamete to the large fixed macrogamete; 

 micronucleus dividing in each (Carchesium). B. Microgamete containing eight micronuclei; 

 macrogamete four ( Vorticella) . C. All but one of the micronuclei have degenerated as polar 

 bodies or " corpuscules de rebut." D. Each of the micronuclei of the last stage has divided into 

 two to form the germ-nuclei ; two of these, one from each gamete, have conjugated to form the 

 cleavage-nucleus seen at the left ; the other two, at the right, are degenerating. 



has given rise to four descendants, each containing a macronucleus 

 and micronucleus derived from the cleavage-nucleus. From this time 

 forward fission follows fission in the usual manner, both nuclei divid- 

 ing at each fission, until, after many generations, conjugation recurs. 

 Essentially similar facts have been observed by Richard Hertwig 

 and.Maupas in a large number of forms. In cases of permanent 

 conjugation, as in Vorticella, where a smaller microgamete unites with 

 a larger macrogamete, the process is essentially the same, though the 

 details are still more complex. Here the germ-nucleus derived from 

 each gamete is in the macrogamete one-fourth and in the microgamete 



