HYALONEMA (HYALONEMA) GRANDANCORA. 239 



spicules of the sponges to which they ai-e attached in their upper parts which he 

 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 m thick. 



The microhexactines (Plate 79, figs. 21-23) are 100-170 ,u in diameter, and 

 have straight, conical, sharp-pointed rays, 3.5-4 yu 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 /u 

 long and 0.5-0.7 n thick. 



From a morphological point of \'iew 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 m 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 fi 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 ,u. The 

 amphidiscs over 250 n in length are those with the broad anchors and more 

 smooth shaft; the amphidiscs under 80 n 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 ii in length, and micramphidiscs with narrower 

 anchors and spiny shaft under 80 /x in length. 



Of the eighty-five macramphidiscs measured one was only 250 ^ in length, 

 the other eighty-four were 318-510 yu. I am not quite sure whether the single 

 macramphidisc only 250 n long is to be considered as a normal amphidisc proj^er 

 to the sponge. Assuming this to be so, two morphologically similar kinds of 

 macramphidiscs may be distinguished, a larger and a smaller, separated biomet- 



' Max Schultze. Die Hyalonemen, 1860, p. 29. 



