262 HYALONEMA (PRIONEMA) AGUJANUM. 



In var. tenuis, form A, I found a remarkable abnormal amphidisc (Plate 75, 

 figs. 35-37), 224 n long with a straight shaft 20 ix thick. One of the terminal 

 anchors is quite regular, 90 /^ long and 112 /i broad; the other is somewhat 

 irregular, and partly spirally twisted. Two large protuberances about 50 n 

 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 ovoid in shape. If this be so, we might assume that 

 the amphidisc 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- 

 phidisc 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 yu long and 75 /j 

 broad; the anchor-shaped spine- verticil of the central tyle is 61 m long and 55 ^ 

 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 



