76 CALYCOSILVA CANTHARELLUS. 
The ordinary rhabds (Plate 1, figs. 1-4; Plate 2, figs. 1b, 12b; Plate 5, figs. 
1, 2, 4, 8, 9, 11-16) are more or less, sometimes very considerably curved, usually 
in a somewhat wavy manner. They attain a length of 2.2-9.1 mm. and a 
thickness of 5-80 4. The ordinary stout rhabds, which are found in small 
numbers in the region of the junction of the stalk to the body proper, are in 
C.c. var. helix 45-55 u thick, in C. c. var. simplex 55-80 u. The ordinary slender 
rhabds, which form the paratangential bundles in the floors of the subdermal 
and subgastral cavities and which traverse the choanosome obliquely and trans- 
versely in large numbers, are 2.2-6.2 mm. long and 5-23 yu thick near the middle. 
They are in C. c. vars. megonychia and simplex on the whole somewhat thicker 
than in C.c. var. helix. Forms intermediate between the stout rhabds mentioned 
above and these slender ones occur, but they are rare. The longest rhabd ob- 
served, which measured 9.1 mm. in length, belongs to these intermediate forms. 
In these rhabds a longitudinal main axial thread is observed, which termi- 
nates just below the two ends in the adult spicules, but opens out freely, with a 
funnel-shaped widening, in some at least of the young. Besides this there are 
two short rudimentary axial threads, forming a cross. The two rudimentary 
axial threads are usually 1.5-4 » long. Very distinct rounded protuberances 
arise over most of the slender rhabds (Plate 1, figs. 3, 4; Plate 5, fig. 9). These 
protuberances are generally very low, lower than broad, and in that case the 
spicule appears as a centrotyle. Exceptionally they attain a greater length, and 
in that case the spicule appears as a tri- to hexactine, with two long rays, and 
from one to four perfectly smooth, terminally rounded, cylindrical, rudimentary 
rays. The longest rudimentary ray of this kind observed measured 38 yw in 
length. In some of the slender rhabds the central tyle is so small as to be 
hardly or not at all discernible (Plate 5, fig. 8). Hardly or not at all centrotyle 
rhabds are much more frequent among the thicker than among the slender 
rhabds and most of the thickest are not centrotyle at all. Twenty slender rhabds 
of C. c. var. helix which I measured were 7—20 » thick in the middle, close to the 
central tyle, which measures 10-23 » in diameter. In these spicules the central 
tyle was 1-7 u thicker than the adjacent parts of the spicule. This difference is 
correlated to the thickness of the spicule only in so far as it is on the whole some- 
what smaller in the thicker than in the thinner rhabds. 
Most of the ordinary rhabds are more or less anisoactine amphistrongyles 
or very blunt amphioxes (Plate 5, figs. 2, 12, 13). Their ends are usually about 
a third to a half as thick as their central part. Sometimes a slight spindle-shaped 
thickening is observed just below the end. Occasionally (Plate 5, figs. 14, 15) 
