THE PROPERTIES OF PROTOPLASM. 69 



toplasm is the oldest, most primordial, and most important constituent. 

 In every real cell there is, besides protoplasm, and while still alive and 

 independent, a second important constituent, the cellular germ, so 

 called (nucleus or cytoblast) ; but even this germ consists of an albu- 

 minous chemical compound which is closely related to protoplasm, 

 and was orginally produced from it by an exceedingly slight chemi- 

 cal alteration. The germ is usually a smaller and firmer formation 

 within the protoplasm of the cell. 



Inasmuch as the idea of an organic cell, as now adopted by liistol- 

 ogists, rests on the presence of two different essential parts in this 

 elementary organism, the internal cell and the external protoplasm, 

 we must distinguish also two diiferent kinds of elementary organisms : 

 germless cytods, as moners for example, and the real germ-inclosing 

 cells, which originate from the former by secreting in the interior of 

 the small mass of protoplasm a true germ or nucleus. Cells of the 

 simplest kind consist only of protoplasm with a nucleus, while in 

 general the cells of animal or vegetable bodies have also other con- 

 stituents, particularly and frequently an inclosing skin or capsule (the 

 cellular membrane), also crystals, grains of fat, pigments, and the like, 

 within the protoplasm. But all of these parts came into being only 

 secondarily through the chemical action of protoplasm ; they are but 

 the internal and external products of pi'otoj^lasm. (Haeckel's " Gene- 

 relle Morphologie," vol. i., p. 279). The single cell of the simplest 

 kind is able to exist as an independent organism. Many of the lowest 

 plants and animals, and also many neutral protista (which are neither 

 animals nor plants), retain for life the character of a simple cell. Such 

 unicellular organisms of the simplest kinds are the amcebce, found in 

 large numbers as well in fresh as in salt water. Amoebae are simple 

 naked cells of various and varying forms. The whole difference 

 between them, especially ^:>ro<am56e, and certain moners, is that they 

 have a germ. It is probable that tliis germ of the amoebae (as may 

 be supposed to be the case with many and perhaps all other cells) is 

 only an organ of propagation, and hence of heredity; while all the 

 other functions, alimentation, motion, and sensation, are performed 

 by the protoplasm. This seems to indicate that at the reproduction 

 of the cells, which is usually effected by segmentation, it is the germ 

 which first divides in two, and that the protoplasm afterward gathers 

 around each of the two sister germs till it also falls in two. It is 

 impossible to distinguish from the common amoebae the cellular ovules 

 of many of the inferior animals, as for example the sponges, medusae, 

 and other plant-like animals. With these the eggs are simple naked 

 cells, which, with the sponges especially, sometimes crawl about inde- 

 pendently in the body of the animal, giving rise to the idea that they 

 were a class of parasitic amoebae. But with other animals also, and 

 with most plants, the eggs of which generally obtain subsequently 

 special and often very complicated encasements and other additions, 



