1897] FUNDAMENTAL PRINCIPLES OF HEREDITY 307 



In some forms that are in other respects very primitive, we tind 

 a true differentiation that has advanced further than Protospowjia, 

 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 filially 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. 

 Prom 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 



