divergent rays, forming a triple fork, and corôÙreôÙsponôÙding (after a fashion {472} which we have already described as occurring in certain sponge-spicules) to the three superficial furrows between the adjacent cells. This last is, as it were, an intermediate stage between the simple rods and the complete formation of another concentric sphere of latticed hexagons. Another possible case is when the large and uniform vesicles of the outer protoplasm are mixed with, or replaced by, much smaller vesicles, piled on one another in more or less concentric layers; in this case the radiating
Fig. 226. Fig. 227. A Nassellarian skeleton, Callimitra carolotae , Hkl.
rods will no longer be straight, but will be bent into a zig-zag pattern, with angles in three vertical planes, corôÙreôÙsponôÙding to the successive contacts of the groups of cells around the axis (Fig. 226).
Among a certain group called the Nassellaria, we find geometrical forms of peculiar simplicity and beauty,ãsuch for instance as that which I have represented in Fig. 227. It is obvious at a glance that this is such a skeleton as may have been formed {473} (I think we may go so far as to say must have been formed) at the interfaces of a little tetrahedral group of cells,