238 THE PROTOZOA 



form four daughter-nuclei, of which one only remains active, while the 

 other three degenerate and disappear. The active daughter-nucleus 

 divides again and one of the resultant nuclei migrates to the other 

 organism, while the other resultant nucleus remains quiescent. The 

 migrating nucleus in each conjugant unites with the quiescent nucleus 

 of the other individual, and thus effects fertilization, after which the 

 organisms separate (Fig. 131). 



The three daughter-nuclei (corpuscules de rttui) which are elimi- 

 nated in each individual before the union of the "germ nuclei," are 

 undoubtedly analogous to the polar bodies of the Metazoa. The 

 agreement in number with the polar bodies of the Metazoa is inter- 

 esting, but it may be doubted whether this agreement has any real 

 significance, for the number of nuclei eliminated in other genera of 

 Ciliata varies considerably, e.g. Vorticella} 



Mark ('82), followed by Butscbli ('85), explained the formation of 

 polar bodies in the Metazoa as aborted eggs resulting from the 

 attempt to form many individuals as the early sperm cells do, and 

 the latter regarded it as a reminiscence of the colony-formation of the 

 Protozoa, basing his view upon the sexual relations of Volvox and Pan- 

 dorina (see above), while Hartog ('91) expressed a somewhat similar 

 view in the statement " the page of morphological history, revealing 

 that the oogamete was primitively one of a brood of at least four, 

 has not been obliterated from the ontogenetic records of the 

 Metazoa." 2 



Richard Hertwig('98), after summing up the evidence in Protozoa 

 of the homologue of polar bodies, came to the conclusion that in 

 all cases there is probably a double division before, after, or during 

 fertilization, which represents a physiological condition of the cell 

 and without phylogenetic significance. Excepting for the Infusoria 

 the double division is, however, established in only one form {Actino- 

 sphcerium), and it is rather difficult to believe that observations 

 have been incomplete in all other reported cases where only one 

 such division is found. Hertwig's view, however, that the preliminary 

 division of the nuclei prior to fertilization represents a physiological 

 condition of the protoplasm, is in no way opposed to the facts in 

 Protozoa. 



Up to the present time no such structures as tetrads have been found 

 in any Protozoa ; indeed, in only a few cases have chromosomes been 

 observed, and then they are so numerous as to render counting im- 

 possible. Hertwig ('89) somewhat doubtfully asserted that the num- 

 ber of chromosomes in Paramcecutm caudatum is reduced from 8 or 9, 

 to 4 or 6, and, again ('98), he maintained that in Actinosphcerium the 



1 Cf. Maupas. ' 2 I.e., page 66. 



