ON PHORONIS OVALIS, STRE I'HILL WEIGHT. 
119 
is probably Poly cl ora. The Sponge forms much larger 
cavities than those produced by the Phoronis, and these 
naturally have a form corresponding with the lobes of the 
Sponge, being quite different in shape from the cylindrical 
Phoron i s-tubes, which remain of approximately the same 
diameter throughout their course. The Polychsete tubes are 
larger than those of the Phoronis; and, instead of having 
the hyaline character of the tubes of this organism, their 
transparency is affected by the presence in them of numerous 
granular particles. 
The tubes of the Phoronis are represented in several of 
the figures (e.g. PI. 8, fig. 15; PI. 9, fig. 37). It will be 
seen that they are by no means uniform in shape, but that 
they are generally curved in various ways. The thin mem- 
branous tube is closely applied to the inner surface of the 
excavation in the shell, and the burrows are accordingly 
curved in correspondence with the form of the tubes seen in 
a decalcified preparation. 
The most superficial examination of a number of the tubes 
set free by decalcifying the shell shows that there is an 
extraordinary amount of variation in the included organisms. 
It is hardly going too far to say that it is difficult to find two 
individuals alike on a slide containing a large number of 
individuals. The length of the animal varies within wide 
limits, while differences in the transverse diameter of the 
specimens are also marked. The most striking differences 
are seen, however, in the extent of the development of the 
lophophore. While some of the individuals are provided 
with a lophophore bearing well-developed tentacles (PI. 7, 
figs. 1—3), the lophophore is completely absent in others 
(PI. 9, figs. 29, 30). In others again a lophophore in an 
early stage of development can be made out at the distal 
end (PI. 8, fig. 13) ; while all stages between this and the 
fully-developed lophophore can be found without difficulty 
among the other individuals on the slide (PI. 7, figs. 5, 4, 8). 
It is impossible to interpret these appearances on any other 
supposition than the assumption that regeneration of the 
