334 THE VOYAGE OF H.M.S. CHALLENGER. • 



and siiKiU spaces, and extended continuously over the spaces aud openings. No wide 

 gastral cavity or oscular opening is to be recognised. 



The microscopic examination of the dictyonal framework reveals a somewhat irregular 

 network of l^eams which are beset with moderately large smooth tubercles of irregular 

 number and arrangement. The beams never exhibit a spherical thickening of the nodes 

 of intersection. In dead portions the axial canals of the dictyonal hexacts are here and 

 there greatly enlarged, and accordingly well marked. The dermal skeleton consists 

 chiefly of moderately large, smooth, or only terminally somewhat tubercled pentacts, 

 which form by their apposition a beautiful square meshed lattice-work. In addition to 

 this, bundles of fine spicules pointed at both ends jut out, and scopulse of different 

 forms occur, but especially forms provided with rough pointed shafts and four strong, 

 almost or absolutely parallel teeth, densely beset with barbs. These teeth spring 

 from a simple conical expansion of the shaft, and possess no knob-like terminal swellings 

 (PL XCII. fig. 5). 



On the surface of the large inner strands and plates of the dictyonal fibrous frame- 

 work there are no pentacts, but only scopulse, and unpointed fine spicules which also 

 appear to constitute the skeleton of the gastral membrane. 



In the parenchyma, and between the reticulated beams of the dictyonal framework, 

 there are uncinates, which usually exhibit a slight curvature, and further, those spicules 

 which are characteristic of the genus Cyrtaulon and were first described by Oscar 

 Schmidt, who regarded them as discohexasters with a greatly prolonged ray. These 

 forms exhibit a simple shaft, which runs out to a fine point, and is provided on the 

 pointed terminal portion with rough knobs ; on the other extremity with a knob- or 

 ball-like thickening, wliich bears a somewhat large number of thin terminal rays with 

 terminal discs. The thickening which occurs close beneath the pointed extremity of the 

 arrow-like shaft in Cyytaulon ( Volvulina) sigsbeei is here entirely wanting. This peculiar 

 form of spicule may be best regarded as a modification of a hexaster, but I have not found 

 any indications of the basal parts of principal rays, except the long shaft. All the thin 

 terminal rays originate directly from the knobbed terminal thickening of that shaft. 

 In addition to the scopulte with four thick rough teeth, already mentioned in the dermal 

 skeleton, other forms with four thin smooth teeth and simple terminal knobs apparently 

 occur in the parenchyma, in addition to those which bear six thin smooth similar ter- 

 minal rays with terminal knobs or discs (PL XCII. fig. 6). If one imagines the numlier of 

 these teeth to be increased and their position more irregularly radial, one can also under- 

 stand the unusual form of parenchymalia. I have not found any regular hexacts in 

 Cyrtaulon sohdus. 



