1897) FUNDAMENTAL PRINCIPLES OF HEREDITY 307 
In some forms that are in other respects very primitive, we find 
a true differentiation that has advanced further than Protospongia, 
the lowest animal type we have selected as an illustration. Volvox 
globator is a beautiful green sphere the size of a small pin’s head, 
found actively rolling over and over, as its name implies, in still 
waters fully exposed to the light. On microscopic examination it 
is seen to consist of many hundreds or even thousands of green cells 
imbedded in the surface of a spherical mass of gelatinous cellulose, 
and sending their active lashes into the water. Scattered among 
these are a few larger cells, which may be seen in all stages of 
segmentation ; and as these grow and segment, they protrude into 
the cavity of the sphere, and finally rupture it and become free as 
new individuals. The ruptured sphere sinks to the bottom, and the 
colonial cells at its surface soon die, whether from the unfavourable 
conditions or no it is impossible to say. At the time for pairing it is 
only the few large cells that become or give birth to pairing-cells ; the 
resulting coupled-cell segments to form a new colony. Here again 
we have a well-marked sterilisation of tissue-cells, and their characters 
are transmitted only through the reproductive cells, their collaterals. 
From our standpoint Volvox must rank as a lowly Metaphyte. 
The majority of Metaphytes show a much higher differentiation 
and a power of colonial propagation far greater and more continu- 
ously exercised than in any Animals, 
The first that we shall consider are the Scale and Leaf-mosses. 
As is well known, the little capsule or urn is full of a fine dust con- 
sisting of reproductive brood cells or ‘spores.’ These germinate and 
grow, as in Protophytes, into filaments consisting of elongated cells, 
some of which are green and run on the surface of the ground, while 
others penetrate it and serve as roots. But so little specialised are 
they that the reversal of a minute sod containing them will deter- 
mine a change of their relative character and functions. On branches of 
these other cells are formed, which are short and thick. These divide, 
and by their colonial growth the proper leafy moss-plant is formed, 
but only the lower part for the time being assumes the condition of 
the moss tissues, the uppermost cells being colourless, nourished by 
the green cells of the stem and leaves, and assuming and retaining 
the functions of an embryonic tissue. This constitutes the ‘ growing 
point’ characteristic of all the higher plants. 
Ultimately, in the deeper parts of certain outgrowths, near the 
growing point, are formed reproductive-cells which give rise to 
pairing-cells, male or female, as the case may be. Fertilisation is 
internal, the male cell swimming up to the immovable female, and 
fusing with it in situ. The coupled-cell remains imbedded in 
the Moss-plant, and is nourished thereby as a parasite, and, 
undergoing segmentation, is converted into a colonial mass. The 
