86 BIOLOGICAL LECTURES. 



tory for some solid products of cell-metabolism, under certain 

 circumstances, just as the spaces in the cell-body are used for 

 such a purpose. And thus sonic of the bodies included under 

 the generic name of nucleolus, may belong to the group of 

 metaplasm. It is, however, difficult to pass any definite 

 opinion on the nature of the nucleolus at the present stage 

 of our knowledge on the subject. 



To recapitulate briefly, then, the chromosome and cyptoplasm 

 are the two active, living constituents of the cell. The rest of 

 the bulk of a cell consists of non-living substances, which have 

 yet to be converted into vital elements, or are the products of 

 metabolism which have now lost the distinctive characteristic 

 of a living substance. 



The behavior of the cytoplasmic thread or network suggests 

 that it is formed of a group of small, living particles, each 

 with the power to assimilate, to grow and multiply by division. 

 The chromosome, in the same way, is itself a colony of 

 minute organisms of another kind, each endowed with similar 

 attributes of vitality. The media, in which they live, — the 

 cytolymph and caryolymph — are the media in which they 

 breathe, from which they derive their nourishment, or within 

 which they deposit the products of their metabolism. The 

 reason why the cell as a whole assimilates, grows and divides, 

 is ultimately due to the fact that the minute particles which 

 compose the cytoplasm and chromosome are endowed with 

 these functions. 



Keeping in mind then such a simple nucleated cell like 

 an amoeba or an animal ovum, as a type, let us ask ourselves 

 the following questions : What is the relation of nucleus^ to 

 cytoplasm, and of cytoplasm to nucleus in a cell .' What is 

 the significance of this duplex morphological organization .-* 

 Through what process may such an organization as the 

 nucleated cell be considered to have come into existence.-* 



The biogenetic law as applied to the stud)' of metazoan 

 organisms, has been an important instrument of research in the 

 field of comparative anatomy and cmbrvologv. but it is hard to 



^ In the following, the word " nucleus " is used, unless otherwise stated, 

 synonymous with its essential constituent, the " chromosome." 



