GROWTH AXD REPRODUCTION. 



205 



halve its mass, gain new surface, and restore the balance. Here, in 

 fact, the famous law of Malthus holds good. 



III. Cell-division. — What usually occurs, then, at the maxi- 

 mum or limit of growth, is that the cell divides. This, in its simplest 

 forms, is rough enough to suggest rupture or overflow ; but in the 

 vast majority of cases it is an orderly and definite process, in which 

 the nucleus plays an important and probably a controlling part. By 

 a complicated series of changes, both in form and position, the 

 essential nuclear elements group themselves so as to form the daugh- 

 ter-nuclei of each product of division. The orderliness and complexity 

 of these changes forbid any offhand attempt to analyze the real 

 physiological movement by which the growth of all multicellular 

 organisms is effected. That attractions and repulsions do exist within 



c. 



Fi<;. 78. — Diagram of the changes in the nucleus during cell-division : — coil stage (,1), 

 the formation of a double star (fi, c, d), and the recession of the divided 

 chromatin elements to opposite poles (<•) to form the daughter-nuclei (/) 

 of the two daughter-cells. — From Hatschek, after Fle:;:ming. 



the cells is certain ; an analysis of their precise nature — the final 

 problem of histology — is still far in the distance. We can not get 

 within miles of it. The problem has always loomed before embry- 

 ologists and histologists — the historians and mechanicians of the 

 organism. Pander, in the first quarter of this century, was inquiring 

 into the mechanics of development, and Lotze followed him with some 

 luminous suggestions. The task has been continued by His and 

 Rauber ; while the experimental investigations of O. Hertwig, Fol, 

 Prliiger, Born, Roux, Schultze, Gerlach, and others, have added 



