SEXUAL PHENOMENA IN THE PROTOZOA 233 



Protozoa, retain the power to renew their vital activities, and with it 

 the possibility of continued existence. Thus, the penalty of speciali- 

 zation appears to be death. 



B. THE SO-CALLED MATURATION-PHENOMENA IN PROTOZOA 



It is now a well-established fact that in the higher plants and 

 animals the nuclei of the germ-cells, when ready for fertilization, 

 contain only one-half as many chromosomes as the nuclei of the body- 

 cells. This discovery, made by Van Beneden ('83), has been so 

 widely extended in the animal and vegetable kingdoms that it is now 

 generally regarded as a necessary condition of the union of sex-cells ; 

 for by this union, it is argued, the number of chromosomes would be 

 doubled were it not for the preliminary reduction to one-half. The 

 phenomena leading to reduction of the chromosomes to one-half the 

 number characteristic of the species are known as the maturation or 

 reducing phenomena. In the egg the nucleus divides twice, while 

 near the periphery of the cell, and two minute cells, abortive eggs or 

 polar bodies, are formed, which degenerate and disappear without 

 further action. In the spermatozoon all of the four cells, which are 

 formed by a similar double division, are functional. In both egg and 

 spermatozoon one division of the nucleus, at least, results as in 

 ordinary mitosis, in the equal partition of each chromosome. The 

 chromosomes at this period frequently differ in appearance from 

 the ordinary chromosomes, and from their peculiar shape are known 

 as tetrads ( Viercrgruppen'). At this point, however, the various 

 observations differ and an animated controversy, which began with 

 Weismann, is still vigorously maintained in regard to the exact way 

 in which these maturation-chromosomes are formed and divided. 

 The controversy, which in large part involves Weismann's specula- 

 tions upon heredity, need not detain us here, however, for with the 

 Protozoa, only the general aspects of reduction are in question. 1 



In the Protozoa, with the somewhat doubtful exception of Para- 

 mcecium caudatum (Hertwig, '89), there is no case on record of 

 reduction in the number of chromosomes, and even in the few cases 

 where actual chromosomes occur, their number is so great that 

 counting is impossible. There are, nevertheless, certain phenomena 

 antecedent to conjugation in Protozoa which warrant the belief that 

 processes take place, even in these primitive animals, which are 

 analogous to the formation of polar bodies in the Metazoa. In 

 general, these processes consist in the elimination of one or more 

 daughter-nuclei prior to conjugation, and are usually the same for 

 both conjugants. 



1 For a discussion of the problems of reduction, see Wilson, The Cell, 2d ed., 1900, p. 233. 



