HYALONEMA (HYALONEMA) GRANDANCORA. 239 
spicules of the sponges to which they are attached in their upper parts which lie 
close to the sponge-body.'! In the Palythoae investing the stalks of Hyalonema 
(Hyalonema) grandancora, on the other hand, the armour is composed entirely of 
spicules of the sponge on which they grow. In these cases therefore the sym- 
biosis appears to be considerably closer than in the Hyalonema symbiont zoan- 
thid above referred to, which were examined by Max Schultze, Bowerbank, 
and R. Hertwig. 
The stalk-spicules. The parts of the stalk-spicules present in the specimen 
appear as rhabds with various markings on the surface. Near the point where 
they arise from the sponge they are 280-400 u thick. 
The microhexactines (Plate 79, figs. 21-23) are 100-170 yu in diameter, and 
have straight, conical, sharp-pointed rays, 3.5—4 » thick at the base. The rays 
bear spines. These are sparse, large, and situated vertically on their basal part; 
distally they become inclined backwards, towards the centre of the spicule, 
where they are more numerous and smaller. The largest spines are 0.8-1 yu 
long and 0.5-0.7 wu thick. 
From a morphological point of view two kinds of amphidiscs can be dis- 
tinguished: — those with relatively broad and short anchors, and few or no 
spines outside the central tyle on the shaft; and those with more slender anchors 
and spiny shaft. The amphidises are 17-510 uw long. 
Apart from the few amphidiscs with serrated teeth referred to above, which 
are to all appearance foreign, no amphidises over 80 and under 250 u in length 
were found. Thus there is, as the adjoined graph, based on 168 measurements, 
shows, a great gap in their length frequency-curve between 80-250 yu. The 
amphidises over 250 u in length are those with the broad anchors and more 
smooth shaft; the amphidises under 80 u in length are those with the narrower 
anchors and spiny shaft. Thus the morphological distinction between these 
two kinds of amphidises coincides with the biometrical, and I accordingly divide 
the amphidises into two main groups: — macramphidises with broad anchors 
and more smooth shaft over 250 » in length, and micramphidises with narrower 
anchors and spiny shaft under 80 uw in length. 
Of the eighty-five macramphidiscs measured one was only 250 y in length, 
the other eighty-four were 318-510 uw. Iam not quite sure whether the single 
macramphidise only 250 » long is to be considered as a normal amphidise proper 
to the sponge. Assuming this to be so, two morphologically similar kinds of 
macramphidises may be distinguished, a larger and a smaller, separated biomet- 
' Max Schultze. Die Hyalonemen, 1860, p. 29. 
