ii2 Darwin, and after Darwin. 



colonies of Protozoa. And its marvellous development 

 in the Metazoa appears ultimately to depend upon the 

 highly specialized character of germ-cells. Even in 

 cases where multicellular organisms are capable of re- 

 producing their kind without the need of any preceding 

 process of fertilization (parthenogenesis), and even in 

 the still more numerous cases where complete or- 

 ganisms are budded forth from any part of their parent 

 organism (gemmation, Fig. 28), there is now very good 

 reason to conclude that these powers of a-sexual 

 reproduction on the part of multicellular organisms 

 are all ultimately due to the specialized character of 

 their germ-cells. For in all these cases the tissues of 

 the parent, from which the budding takes place, were 

 ultimately derived from germ-cells no matter how 

 many generations of budded organisms may have 

 intervened. And that propagation by budding, &c., 

 in multicellular organisms is thus ultimately due to 

 their propagation by sexual methods, seems to be 

 further shown by certain facts which will have to be 

 discussed at some length in my next volume. Here, 

 therefore, I will mention only one of them and this 

 because it furnishes what appears to be another 

 important distinction between the Protozoa and the 

 Metazoa. 



In nearly all cases where a Protozoon multiplies 

 itself by fission, the process begins by a simple 

 division of the nucleus. But when a Metazoon is de- 

 veloped from a germ-cell, although the process likewise 

 begins by a division of the nucleus, this division is not 

 a simple or direct one ; on the contrary, it is inaugurated 

 by a series of processes going on within the nucleus, 

 which are so enormously complex, and withal so 



