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Chas. B. Wilson 



medium« (Hertwig) is closely connected with rapidity of develop- 

 ment. 



We can easily see that this must be so, for the rapidity varies 

 with the relative amount of active protoplasm which the egg contains. 

 Any given influence, therefore, will produce very different results 

 according as it is exerted upon eggs having a large quantity of such 

 protoplasm, or upon those possessing only a meagre amount. 



A second fact is one already stated by Hertwig. The » lower- 

 ing of the energy in the different parts of the egg is not equal 

 but regulates itself according to the proportion in which the active 

 protoplasm substance and the more passive nourishment material 

 are contained in the egg cavity «. This fact appears in every 

 experiment with the three species now being considered as plainly 

 as with the two species of Kana upon which Hertwig experimented. 



A third fact follows in logical sequence i. e. the effect produced 

 by the surrounding medium does not depend upon the absolute 

 amount of active protoplasm which the egg contains, nor upon the 

 relative amount compared with its size, but upon the relative amount 

 contained in the animal half compared with the vegetative half 

 The large Amblystoma eggs contain relatively a smaller amount of 

 this active substance than the small Chorophilus eggs. Consequently 

 their ordinary development is much slower, and they are retarded 

 more by the restraining influence of the same medium. But there 

 is less difference between their animal and vegetative cells in the 

 amount of active protoplasm which each contains than is found in 

 the more rapidly developing Chorophilus eggs. In consequence of 

 this, the influence of the solution is more nearly equal upon the 

 two kinds of cells. The both lie dormant for a time, and although 

 the animal cells recover first they do not develop rapidly enough 

 to prevent the vegetative cells from recovering in their turn and 

 following them at a comparative rate approximately normal. 



On the contrary, in the eggs of Chorophilus there is a great 

 difference iu the amount of active protoplasm contained in the animal 

 and the vegetative cells. Consequently when brought under the 

 influence of a restraining medium there is an increased difference 

 in the effects produced upon the two kinds of cells. The animal 

 cells have so much activity that they seem scarcely restrained at 

 all, but continue to develop at nearly the normal rate. But the 

 vegetative cells, possessing only a little active protoplasm are 

 restrained so much that they can scarcely continue at all, or may 



