262 HYALONEMA (PRIONEMA) AGUJANUM. 
In var. tenuis, form A, I found a remarkable abnormal amphidisc (Plate 75, 
figs. 35-37), 224 » long with a straight shaft 20 1 thick. One of the terminal 
anchors is quite regular, 90 1 long and 1124 broad; the other is somewhat 
irregular, and partly spirally twisted. Two large protuberances about 50 y» 
long arise from the rather eccentrically situated “‘central”’ tyle of the shaft. 
One of these terminates in a broad and thin lamella extending in a radial plane 
which passes through the axis of the spicule. The distal part of this lamella is 
strongly and abruptly bent, so as to become parallel to the shaft (Plate 75, fig. 35). 
The other protuberance of the central tyle terminates in a stout oblique spine. 
If we mentally construct an ovoidal (rotation-ellipsoidal) surface following 
the outer sides of the teeth of both anchors and entirely enclosing the whole 
spicule, we find that the large protuberances of the central tyle reach this surface 
and abruptly bend on reaching it. This indicates that such an ideal rotation- 
ellipsoidal surface formed a real limit to their radial growth. This limit may very 
likely be the surface of a cell ovoidin shape. If this be so, we might assume that 
the amphidise was formed and grew within this cell, and that the outer band- 
shaped parts of its anchor-teeth and the distal bent parts of the protuberances 
of the central tyle were developed in the superficial part of the protoplasm of 
this cell. Thus the appearance of this abnormal macramphidisc is in favour of 
the view that each amphidisc is produced, like the sigms and cheles of the monax- 
“onid sponges, in an ellipsoidal cell, the shape of the surface of which determines 
the shape and position of the anchor-teeth, which are formed and which grow in 
its superficial part. 
The serrated amphidiscs (Plate 74, figs. 1-9; Plate 75, figs. 1, 2, 22, 23; 
Plate 76, figs. 33, 35, 36; Plate 77, figs. 2-7) have a rather slender, straight or, 
rarely, slightly bent (Plate 74, fig. 5) shaft. The shaft is considerably thickened 
at or near the middle to a conspicuous central tyle. A verticil of long, more or 
less, often very considerably curved, cylindroconical and truncate or terminally 
rounded spines arises from the central tyle. In an abnormal serrated macram- 
phidise of var. tenuis, form A, the spines of the central tyle are in shape and 
position similar to the teeth of the terminal anchors, only smaller. One of the 
terminal anchors of this spicule (the other is broken off) is 117 » long and 75 u 
broad; the anchor-shaped spine-verticil of the central tyle is 61 » long and 55 yu 
broad. The remaining parts of the shaft are covered rather densely with minute 
spines. These increase in number and in size towards the ends of the shaft. 
The terminal anchor usually consists of eight teeth. The individual teeth are 
generally curved in the same direction, concave to the shaft, throughout their 
length. More rarely a portion of a tooth is curved the other way, convex to the 
