264 Causes and Course of Organic Evolution 



delphia. S. nitida divides its cells very regularly each night 

 from late April till October or even November, and so forms 

 about 230 divisions on the average. In late March and early 

 April a few divisions occur, followed by conjugation, in the 

 second to the third week of April. H. longata shows a similar 

 rate of division, but conjugates a week to ten days earlier than 

 the last. S. maxima after similar dividing activity conjugates 

 in the first to the second week of September. 



An enormously wide field of study is here opened in algoid 

 phytophenology, and which has as yet been little cultivated. 

 But not a few observations tend to show that division, and 

 even more sex-cell formation, is largely dependent on environal 

 conditions, just as is growth and fertilization amongst flowering 

 plants. Thus Oltmanns states for Coleochcete pulvinata that 

 formation of sex-cells takes place in the waters of low ground 

 during July to August, while in mountain lakes it occurs during 

 October to November. 



If we may now quote an illustrative case from animals, it 

 can be said that, though exact observations are still limited 

 mainly to the Infusoria, it is true for some of these, and probably 

 is fcrr many, that, after a definite period of di^dding activity, 

 this is followed by differentiation of the cell contents into 

 complemental gamete cells, with or without a previous rest 

 period. Thus after 170 normal divisions in Paramoecium 

 (Joukowsky), after 175 in Stylonychia (Maupas), and after 

 235 in Oxytricha (Woodruff), a marked cessation of dividing 

 activity takes place, followed soon after by death of the mass 

 of organisms. In other words the supply of some kind of 

 energy that behaved like a disruptive or expansive energizing 

 discharge seems to become so reduced or enfeebled in amount 

 as to fail further in stimulating to division. But Calkins 

 and others since have shown that change in the diet, or supply 

 of certain salts, or special stimulation by such a complex com- 

 pound as extract of pancreas {105: 136) may reestablish what 

 might be called a recharged state of the organism. Then 

 division may be carried on to the 620th or even to the 742nd 

 generation. 



