OTHER THEORIES OF SPECIES-FORMING. 219 



an the germ-cells until, after fertilisation, the egg-cell begins its 

 development. Then as the cells of the new organism begin to be 

 produced, the gemmules become active and each one moves into 

 the cell it should control and there directs its further development 

 into precisely the kind of cell it should be at precisely the time it 

 .should be this kind of cell, until there results from this gemmule- 

 controlled development a photographic reproduction of the parent 

 body. 



Nageli's conception is that when the complex life-characterising al- 

 buminous substances took their birth in an aqueous liquid, they would 



Nageli's be precipitated, as they are not soluble in water. This 



theory. precipitate is formed of small masses, a sort of organic 



crystals, which may be called micella;. And just as an inorganic 

 crystal deposited in a saturated saline solution of the same nature 

 determines the deposit on its surface of the dissolved molecules in 

 the form of little crystals, and by this means grows, so wherever 

 any micellae are formed they facilitate within their sphere of influ- 

 ence the precipitation of others, so that this production of micellae 

 instead of taking place miscellaneously through the liquid will be 

 localised at certain points. Thus arise aggregates of albuminous 

 substance, in the condition of micellae, forming the primitive 

 protoplasm. The micellae, although insoluble in water, have a great 

 affinity for it, and each one at the time of its precipitation fixes 

 around itself a thin layer of water, at least as thick as a water 

 molecule. Thus, all the micellae grouped together in a bit of primi- 

 tive protoplasm are separated from each other, and also held to- 

 gether by a layer of water as thick as two water molecules. This 

 water forms an integral part of the protoplasm. By virtue of it, an 

 aggregate of albuminous micellae can increase by intercalcation as 

 well as by the addition of new micellae on the outer surface. By 

 admitting more or less water the protoplasmic mass may become 

 more or less nearly fluid. Thus are accounted for the various 

 densities always met with in the different parts of a protoplasmic 

 cell. 



A further essential part of Nageli's theory is an arrangement of 

 the primitive protoplasm in two ways, resulting in two kinds of it, 

 which are called nutritive plasm and idioplasm respectively. This 

 arrangement depends on the molecular forces pertaining to the 

 micellae, and the difference, resulting in two kinds of plasm, depends 

 upon the relative situation of the micellae composing the mass, just 

 how this affects them differently, however, not being made very clear. 

 But the differentiation is very important, for it is the idioplasm 

 alone which contains the essential life-properties and which really 

 .gives rise to life with all its variety and complexity. This idioplasm 



