126 
SIDNEY E. HARMER. 
P. ovalis in great detail. I confine myself, therefore, to 
a description which is sufficient to show that the subject of 
this paper is rightly referred to Ph or on is, and also brings 
out some of the more noteworthy features of P. ovalis. 
Tube. 
The characters of the tube can be readily examined after 
decalcification of a fragment of the shell containing the 
animals. The single shell which furnished the whole of 
the material must have contained hundreds of individuals, 
whose tubes penetrated the substance of the shell in all 
directions. Although accompanied by other boring animals 
(C lion a, Polychasta) there is not the slightest reason to 
suppose that the Phoronis inhabits burrows excavated by 
other organisms. The diameter of its tubes is distinctly 
smaller than those of its associates; and each Plioronis- 
tube closely lines the burrow in which it lies, along the 
whole of its course. De Selys-Longchamps (1907, p. 28) 
thinks that the tube is secreted by the proximal end of the 
ampulla, and that its growth takes place at this end. I have 
no observations to indicate how the boring is effected, but I 
am inclined to think that the main increase in length takes 
place as suggested by that author. The set of tubes shown 
in PI. 8, fig. 15, seems to prove, however, that this explanation 
is not sufficient, and that the faculty of boring and secreting 
a tube is not restricted to the region of the ampulla. The 
figure shows that secondary deposits of tube-material may 
be formed inside the original tube. Some of these are more 
or less curved transverse septa (E, B, E), occurring on the 
proximal side of the ampullar region. Others may be formed 
in an irregularly longitudinal direction, as at L. In three 
places (C, G, J) a lateral opening has been formed on the 
proximal side of a transverse septum, and a new tube has 
grown out at an angle with the original tube. These lateral 
tubes, which will be considered below in the section dealing 
with regeneration, can hardly have been formed by the 
