THE SIGNIFICANCE OF FERTILIZATION 171 



we can come at the present time to an explanation of the physical basis 

 of inheritance. The theoretical conclusions have been strengthened 

 and supported by morphological evidence upon the most widely 

 separated groups of animals and plants, and by experimental evidence 

 in connection with the principle of Mendelian inheritance. 



Such, in brief, is the statement of the modern problem of inherit- 

 ance from the cytological standpoint. Now, what connection has this 

 problem with the protozoa ? The chromosome in a metazoon must be 

 a wonderfully complex element of the cell if there is anything in this 

 physical conception of its organization, for we find that the number of 

 chromosomes in the cells of metazoa does not increase with the hio-h 

 grade of differentiation which we find in the higher animals, and if 

 there is a physical basis for adult characteristics, the few chromosomes 

 of a man must be wonderfully more complex individually, than those 

 of invertebrates like a sea urchin or an earthworm which have approxi- 

 mately the same number. In protozoa the chromosomes, when present, 

 are of enormous numbers, in paramecium at maturation more than 

 200, and the only interpretation, on a purely physical basis, is that each 

 chromosome must represent a simple character, or, at least, a simpler 

 group of characters, than the chromosomes of higher animals. In the 

 more primitive protozoa the physical basis of inheritance (idiochro- 

 midia) is not moulded into definite chromosomes, but is uniformly 

 halved while in granule form. In other words, a study of protozoa 

 chromosomes leads to the theory that chromosomes, the characteristic 

 structures of the nucleus in mitosis, have had an evolution no less 

 surely than has the nervous system, digestive system, or supporting 

 system of the higher animals, and that the chromosomes of the pro- 

 tozoa have the same relation to chromosomes of the metazoa that the 

 organization of the protozoan body has to that of the rnetazoan, i. e., 

 a unit structure. 



F. THE SIGNIFICANCE OF FERTILIZATION. 



It is perfectly obvious that whatever view is taken of the significance 

 of fertilization, it must be sufficiently general to account for the phe- 

 nomena of parthenogenesis, autogamy, and endogamy, as well as for 

 the more complicated processes of exogamy. Biitschli's ('76) early 

 view that conjugation is a process involving rejuvenation (Verjungung) 

 of the individual, while giving no idea as to what the nature of the 

 rejuvenating process actually is, has been but little improved upon by 

 the work of subsequent observers. Maupas' conclusion that nuclear 

 rejuvenescence is alone involved is not wholly consistent with the facts, 

 and his attempt to penetrate more deeply into the mysteries of the 

 matter by defining the conditions of conjugation has been only partly 



