80 THE VOYAGE OF H.M.S. CHALLENGER. 



buudles. The comitiilia, which for the most part compose the fibrous bundles, are, on the 

 other hand, very much prolonged triacts with short transverse rays ; more rarely they 

 are diacts or tetracts. Inferiorly and in the outer part of the longitudinal bands of 

 fibres numerous diacts always occur with abundant barbs and with inferior anchors on 

 whose knob-like thickened extremities an indefinite number of anchor teeth form a pro- 

 jecting wreath. I have not found pentact anchors such as occur in the basal tuft of 

 Euplectella aspergillum (Pi. III. figs. 23). Between the bundles of longitudinal and 

 transverse fibres, which intersect at right angles, oblique or spiral filjrous bands alone 

 occur. These are, on the whole,* somewhat more loosely compacted than those formed 

 from the tetract principalia just described, and consist almost exclusively of very long 

 thin triacts with short transverse rays, and more rarely in part also of diacts and 

 tetracts. Sometimes some sj^iral bands also extend over the outer side of the longi- 

 tudinal and the inner side of the transverse beams, or pass over some longitudinal 

 bands externally, then along their inner side between the longitudinal and transverse 

 beams for a certain distance, again passing outwards, and so on. Since each of the 

 quadrate principal meshes, which are from 3 to 5 mm. in breadth, encloses a circular 

 parietal gap, the obliquely crossed bands of fibres cannot lie along the diagonal line of 

 the meshes, but pass close to the parietal foramina, and assist in forming their margins. 

 In this way a woven mesh work is formed, which — as Marshall has pointed out — somewhat 

 resembles that of our common cane-bottomed chairs. The parenchymalia which lie between 

 the long spicules of the principal bands of fibres are for the most part triacts, pentacts 

 and diacts with slightly bent rays, also small normal hexacts and oxyhexasters less 

 regularly arranged. In general they resemble the corresponding structures of Euplectella 

 aspergillum so completely that I may refer to the description and figures given for that 

 species. It is only in the circular memlirane, which surrounds the parietal foramina, that 

 the parenchymal spicules — as has also been noted by Marshall — present a somewhat 

 difi'erent character, since in this locality and in the neighbourhood of the free margin 

 substantial spindle-like diacts with four or two median tubercles occur in great numbers. 

 These Marshall" has happily designated compass spicules. Passing from the outer 

 portion of the iris-like circular membrane towards the interior, all transitions from 

 the circular hexacts to those peculiarly deformed diacts may be observed. While 

 externally greatly prolonged curved diacts occur beside the isolated strong hexacts and 

 the numerous pentacts, further towards the interior it may be seen that tetracts and 

 triacts of the same strength predominate, while just at the innermost margin compass 

 spicules are almost exclusively found. 



There may also be observed a system of slender dagger-shaped hypodermalia with 



1 The long tetracts which are represented by Marshall in his diagraniatic figure {loc. cit., pi. xv. fig. 54, cc), as 

 principalia of the oblique spicular bands, I have sought for iu vain in this young specimen. 



2 Loc. cit., pi. XV. fig. 57. 



