HYALONEMA (HYALONEMA) GRAND ANCORA. 
239 
spicules of the sponges to which they are attached in their upper parts which lie 
close to the sponge-body. 1 In the Palythoae investing the stalks of Hyalonevia 
( 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 p thick. 
The microhexactines (Plate 79, figs. 21-23) are 100-170 p in diameter, and 
have straight, conical, sharp-pointed rays, 3.5-4 p 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 /z 
long and 0.5-0. 7 p 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 amphidiscs are 17-510 p long. 
Apart from the few amphidiscs with serrated teeth referred to above, which 
are to all appearance foreign, no amphidiscs over 80 and under 250 p 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 p. The 
amphidiscs over 250 p in length are those with the broad anchors and more 
smooth shaft; the amphidiscs under 80 p in length are those with the narrower 
anchors and spiny shaft. Thus the morphological distinction between these 
two kinds of amphidiscs coincides with the biometrical, and I accordingly divide 
the amphidiscs into two main groups : — macramphidiscs with broad anchors 
and more smooth shaft over 250 p in length, and micramphidiscs with narrower 
anchors and spiny shaft under 80 p in length. 
Of the eighty-five macramphidiscs measured one was only 250 p in length, 
the other eighty-four were 318-510 p. I am not quite sure whether the single 
macramphidisc only 250 p long is to be considered as a normal amphidisc proper 
to the sponge. Assuming this to be so, two morphologically similar kinds of 
macramphidiscs may be distinguished, a larger and a smaller, separated biomet- 
1 Max Schultze. Die Hyalonemen, 1860, p. 29. 
