94 BIOLOGICAL LECTURES. 



extremely minute organisms, each with a power of growing, 

 assimilating, and dividing ; and the nucleus, or, more strictly, 

 the chromosomes, a colony of still different forms, each with 

 the same powers, the whole making an organization compar- 

 able to that of the lichen, which is composed of two totally 

 dissimilar organisms ? 



If this be so, then, there are two possible ways of explaining 

 the nature of a nucleated cell ; viz., the Theory of Differen- 

 tiation, such as was held by Haeckel, Auerbach, and several 

 others, and more recently by Verworn l and Wiesner, 2 and the 

 TJieory of Symbiosis, as I have briefly suggested. 



Let us examine the fundamental phenomena of the nucle- 

 ated cell from the standpoint of the symbiotic theory, and, 

 incidentally, point out the inadequacy of the differentiation 

 hypothesis as an explanation of the cell phenomena in general. 



IV. 



Two important activities in the developmental phases of 

 protoplasmic life* are cell-division, e.g., caryokinesis, and cell- 

 fusion, e.g., fecundation. In both cases, the identity of the 

 nucleus and of the cytoplasm is never once lost during the 

 whole series of remarkable changes. There is a continuity of 

 nuclear matter from one phase to another, just as there is a 

 continuity of the cytoplasm through the successive periods in 

 the history of the cell. In other words, the nucleus always 

 originates from a preceding nucleus, and the cytoplasm from a 

 preceding cytoplasm. There is no evidence proving that the 

 nucleus is formed by the process of differentiation from the 

 cytoplasm, nor that the cytoplasm is formed by the differen- 



1 Max Verworn: Die physiologische Bedentung des Zell-kerns, Bonn, 1891, 

 p. 115. 



2 J. Wiesner: Die Elementarstructur und das Wachsthum der lebenden Substanz, 

 Wien, 1892, p. 266. 



3 Following the suggestion brought out by Professor Burdon Sanderson in his 

 discourse on the elementary problems in physiology (Nature, Vol. XT, Sept. 26, 

 1889), it is convenient to divide the protoplasmic activities into two main groups 

 the developmental and the non-developmental. The former refers to those 

 phenomena of the cell which are more especially connected with the development 

 or unfolding of latent character of the germ, and the latter to such functions as 

 respiration, secretion, excretion, etc. 



