164 CONJUGATION, MATURATION, AND FERTILIZATION 



nucleus, and interpreted as a characteristic of the male individual. 

 In this species, also, Prowazek described a union of portions of the 

 two nuclei, the process being much the same as that described by 

 Schaudinn. Phenomena which may be interpreted as parthenogenesis 

 seem to be, therefore, quite widespread among these parasitic flagel- 

 lates, and not only in species of this genus but in allied genera as well. 

 (See Keysselitz, 1906, for parthenogenesis in Trypanoplasma borreli). 

 In view of the possibility of confusing normal parthenogenetic pro- 

 cesses in these various forms of parasites, with involution and degen- 

 eration phases of the vegetative individuals, the various, and usually 

 conflicting, observations on parthenogenesis cannot be accepted as 

 established. On purely theoretical grounds, however, and in view of 

 the processes of autogamy in primitive protozoa and of partheno- 

 genesis in metazoa, it is not improbable that such methods of 

 fertilization may be found among the parasitic protozoa, where every 

 adaptation for preventing extinction of the species has apparently 

 been evolved. 



E. THE PHENOMENA OF MATURATION IN PROTOZOA. 







As Boveri ('90) long since pointed out, the numerical reduction of 

 chromosomes during the maturation of germ cells, first observed by 

 Van Beneden ('83), is no theory, but an accepted fact. Upon this fact, 

 however, a great superstructure of theories has been erected, and 

 around it some of the most fascinating and successful of modern 

 biological researches have been conceived and executed. In con- 

 nection with the higher animals and plants, the early view of Van 

 Beneden, that reduction is simply a process of eliminating one-half of 

 the chromosomes so that the number characteristic of the species may 

 be kept constant when the germ cells unite, has been given up. Sub- 

 sequent research has showTi that, in the maturation period of both 

 eggs and spermatozoa, after elimination in some cases of fully nine- 

 tenths of the nuclear material, the chromatin substance is redistributed 

 in such a way as to warrant the assumption of some deep-seated 

 purpose. In recent years biologists are coming more and more to 

 accept the hypothesis that this purpose has to do essentially with the 

 phenomena of inheritance, and that the orderly rearrangement of 

 chromatin with the ensuing maturation divisions is evidence of the 

 cellular mechanism by which the physical representatives of hereditary 

 characters are minutely halved and distributed. 



While reducing divisions in highly differentiated forms of life, 

 according to this view, have their raison d'etre in the fact that the 

 great multiplicity of characters of an individual must have their physi- 

 cal representatives concentrated at some time in a single cell, reducing 



