MATERIALS FOR A MONOGRAPH OF THE ASCONS. 381 
From the oscular tubes arise, as already stated, numerous 
diverticula (D.), each an outgrowth of the body-wall pushed 
out, so to speak, like a glove-finger. ‘Three stages are seen 
in text-figs. 1, 2, and 3. The triradiates formed in these 
diverticula take on from the first a different arrangement 
from those in the erect oscular tubes. At first the spicules 
are quite confused and irregular in arrangement (z.) As the 
diverticulum continues to grow, however, order emerges from 
chaos, and the triradiates are found uniformly disposed (text- 
figs. 2, 3, and Pl. 21, fig. 108). Hach triradiate has its un- 
paired ray pointing towards the blind end of the diverticulum, 
but at the point of origin of each diverticulum from the 
oscular tube, there can be seen the region (#.) in which the 
chaotic and irregular arrangement of the triradiates is retained 
without any “righting” of the spicules having taken place. 
The arrangement of the triradiates in the diverticula of 
Leucosolenia was first pointed out by Bidder (1891, 
p- 627). 
The diverticula are, of course, lined by collar-cells and per- 
forated by. pores, like the wall of the oscular tube, and it 
cannot be doubted that the water-current which flows in 
through the pores must pass along the diverticula in the direc- 
tion from the apex to the base, finally debouching through 
the main aperture! into the oscular tube and joining the 
current in the latter. Hence it follows that the arrangement 
of the spicules in the diverticula is the same, in relation to 
the water-currents, as it is in the oscular tubes, with the 
exception of the basal region (#.). If the hypothesis that 
the gastral rays are bent by the current applies in the oscular 
tubes, it also apples in the diverticula. 
The primary diverticula thrown out from the oscular tubes 
grow in length and produce secondary diverticula from their 
sides (text-fig. 4, D, d', d*, d’). The formation of a secon- 
1 Woodland in his comparison of the diverticulum to a ‘water cushion’”’ 
(1905, p. 266) seems to have forgotten their aperture into the oscular tube. 
‘To my mind they can no more be compared to water-cushions than can the 
oscular tube itself. 
