71 



The tube-wall is, in the smaller specimen, on an average about 1 mm. thick and 

 perforated by numerous circular parietal apertures, 1-2 mm. wide. These are 

 situated at the bottom of slight, rounded depressions, surrounded by thin annular 

 membranes and regularly arranged in longitudinal and transverse rows, 8-4 mm. 

 apart. The parietal apertures are arranged so regularly because, as is also the 

 case in Euplectella oweni and Euplectella simplex, one such aperture is contained in 

 nearly every mesh of the main tubular supporting skeleton-net, composed of the 

 longitudinal and transverse fibres. 



The distance between the longitudinal fibres is in all parts of the portion of 

 the tube-wall preserved, about equally great. The distance between the trans- 

 verse fibres on the other hand is, as in Euplectella princeps and E. oiceni, smallest 

 above and increases downwards, towards the lower, torn end of the tube. Here 

 and there, where a fibre has recently divided, this rule is "set aside in the. manner 

 described in Euplectella princeps. The main skeleton-net of the tube-wall has 

 quadratic meshes. It is, in consequence of the greater developement of secon- 

 darily apposed silica glueing the comitalia and principalia together, much harder 

 and more resistant in the large than in the small specimen. 



The principalia composing this skeleton-net are exclusively oxystauractines 

 with smooth rays, 60-100 /* thick. The long rays of adjacent stauractines are 

 parallel and lie for some distance quite close together. Generally two to three 

 of these rays extend side by side in the fibres. These principalia are accom- 

 panied and enclosed by numerous triactine and tetractine, more rarely diactine 

 or pentactine, comitalia with very long smooth rays, 10-20 m thick, the pointed 

 ends of which are usually rough or covered with tubercles. It is to be remarked 

 that the spicular fibres forming the main skeleton-net are not, as in ^wjs/ecieWa 

 simplex and other species of Euplectella, so arranged that the longitudinal 

 ones overlie the transverse ones. They are on the contrary interwoven like the 

 strands in a web and thus form a texture, which however is not quite reo-ular, 

 since sometimes the transverse fibres divide into two strands at the crossing 

 points and the longitudinal fibres pass through the slits thus formed. 



The diagonal spicular fibres are more slender but otherwise similar to the 

 longitudinal and transverse ones. The two spiral systems formed by them cross 

 each other at right angles and consist nearly exclusively of triactine and 

 tetractine spicules with long and slender rays. As in Euplectella these fibres 

 extend mostly outside of the main longitudinal and transverse fibres, some of 

 them however are interwoven with the longitudinal fibres so as to form a texture, 

 similar to that in our cane-chairs. 



As in Euplectella the dermal layer is supported by pretty stout, sword- 

 shaped oxyhexactines, and the gastral membrane by oxypentac tines of similar 

 stoutness. 



