Karyokinesis 327 



tissues to replace those worn out; can, if the leg is cut off 

 there, grow and produce a whole new leg, and they do it 

 by a power of control which is ascertained to be carried by 

 the chromosomes. This inheritance of development is thus 

 carefully divided, and a due proportion of every endowment 

 is passed on. Each particle of chromatin is a germ for a 

 definite growth. And thus the new part is built up or re- 

 paired and maintained and in some cases renewed. And in 

 the case of the full and complete egg, which is the germ 

 cell for the whole body structure, all the subordinate parts 

 of the heredity are included, and provided in its chromo- 

 somes. 



To understand this better let us consider the course of 

 cell growth from the beginning of an individual life. The 

 segmenting egg of a frog, or of a bird for example, is a 

 single small cell supplied and served with a mass of 

 nutritious matter, which makes the aggregate comparatively 

 large. It has been fecundated by sexual process; after it 

 had discarded half of its own nucleus, it received a half 

 nucleus from a male sperm, which was a half cell of diminu- 

 tive size, which entered its substance. Now, in suitable 

 environment, chiefly depending upon a condition of ener- 

 gizing warmth, the germ cell divides, in the manner de- 

 scribed as Karyokinesis; but the two cells resulting, remain 

 in contact instead of separating into independence as they 

 would do if of single celled species. Each new cell divides 

 again, and each of these, acting under the regulation of the 

 chromosomes ; and as they divide generally in the direction 

 of the free ends, they form a symmetrical mass or "morula" 

 which is a bunch of cells something resembling a mulberry. 



