78 THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
In mammals (in vertebrates and invertebrates for that matter) the pre- 
maiotic cell consists in its simplest form of a nucleus, and its associated 
cytoplasm. (Figs. I and 9.) During rest the nucleus consists of a coarse and 
irregular network, or foam-like structure, composed of a denser substance 
(linin) within the shreds and patches of which are scattered in an irregular 
fashion chromatin granules. In the spaces between the strands of this com- 
posite network lies a less stainable substance, and there is generally at least 
one large, round mass of staining material, forming the so-called nucleolus. 
The whole nucleus during rest is bounded by a definite membrane. 
The cytoplasm consists of a less refractive cytoplasmic mass surrounding 
the nucleus, and upon ultimate microscopical analysis this substance is found 
to consist of a finer foam-like structure, or network, between the strands of 
which there lie granules of various and non-constant properties and sizes. 
In mammals, and many vertebrates at any rate, there can usually be 
differentiated in the resting cell a small patch of denser cytoplasm, generally 
near some portion of the nuclear membrane. Within this there usually 
appear two, small, highly refractive, bean-shaped bodies, which under certain 
conditions stain distinctly, and differ from the other granules to which allusion 
has been made in that they remain constant in relationship and appearance 
within the resting cell. These bodies are the so-called centrosomes, and the 
denser cytoplasm which surrounds them may be conveniently described by 
using Boveri's term of archoplasm ; the archoplasm and centrosomes together 
being often spoken of as the attraction sphere. (Fig. 9.) 
Centrosomes are, however, not always present in cells. They appear to 
be constant in the tissues of higher animals, and among the lower plants ; but 
they are not present in the cells of many higher plants, either during rest or 
during the active stages of division. They appear in those plants which 
possess them, among the Protozoa, and in maiotic cells, as we shall see, to 
be specially related to motile organs, such as Flagellae. And in general it 
may be said that the more primitive the type of cell, the more prominent the 
centrosomes will be. We are, at any rate for the present, inclined to regard 
them with van Beneden as primitive cell organs ; but organs which in 
numerous instances have become lost. 
All the pre-maiotic cells of the body, or indeed those belonging to any 
part of an animal except the adult sexual glands, multiply chiefly by mitotic 
division, for although amitosis is present in certain tissues, it is often resolv- 
able, as in the case of Leucocytes, into mitosis, which is, as it were, hurried 
over, its mitotic origin being still in evidence. True amitosis is relatively 
rare, and at present obscure, both in its relationships and occurrence. Here 
again the primitive appears to be the more complex. The segmentation of 
the egg is produced by mitotic division. The fission of the Protozoa has been 
shown to be normally mitotic ; while amitosis appears in the glands, and 
highly specialized tissues of the bodies of animals, and plants. 
From the first segmentation of the egg, to the definite formation of the 
sexual glands, the multiplication of the cells forming the whole body is 
carried out by a series of mitosis, which are all of a similar and pre-maiotic 
character ; and a pre-maiotic division in a mammal may be described as 
follows: — 
