REPORT ON THE HEXACTINELLIDA. 135 



strongly developed, smooth oxydiacts, with slight cui-vature or twisting, and on these 

 numerous oxyhexacts, of variable but not verj^ considerable dimensions. In the latter 

 the four tangential rays are tangentiall)^ disposed in the gastral membrane, while the 

 internal, usually longer radial projects freely into the gastral cavity, and the external 

 radial into the subgastral trabecular space. All the rays of the smaller gastral oxy- 

 hexacts run out gradually to a point, and are of approximately equal length, while in the 

 larger gastral oxyhexacts the internal free ray is decidedly longer than the others, so 

 that a dagger-form results. All the efferent canals are clothed internally with small 

 delicate oxyhexacts, in which the inner radial ray projects to a greater or less distance 

 into the canalicular space (PI. LIV. fig. 2). 



The long radially projecting spicules, which arise in a tuft from the terminal pole of 

 each of the numerous lateral and basal papillse, are smooth oxypentacts. Their interior 

 end runs gradually to a point, while the outer terminates in a four-toothed anchor, in 

 which the four cruciately disposed, strongly developed teeth do indeed at first arise at 

 right angles to the shaft, but become more or less markedly curved inwards (PI. LIV. 

 %9). 



The basalia forming the root-tuft only differ from these lateral radially projecting 

 pleuralia in their greater strength and length, and also in the fact that many of them, 

 which have arisen from the curvature of the lower pleuralia, extend no longer quite 

 radially, but are more or less markedly curved downwards (PI. LIV. fig. 1). 



A good general survey of the structure of this species can be obtained by making- 

 sections of the small, pear-shaped buds. A combined diagram representing this is given 

 in PL LIII. fig. 2. It will be seen that the sack-shaped chambers, taken as a whole, 

 make up a much folded layer, which forms the boundary between the water-passages 

 leading from the external skin and those leading into the common gastral cavity. The 

 circular oscular aperture of the gastral cavity appears at a later stage at the broad distal 

 pole of the pear-shaped bud. The bud at the same time pushes itself outwards on the 

 bundle of pleuralia belonging to the papiUa. It forms for itself papillae w^th pleural and 

 basal tufts of spicules. Finally it becomes detached and rooted in the mud. 



As in the above-described genus, Lanuginella, the basalia (and pleuralia also) are 

 nothing but long drawn-out and protruded spicules of the hypodermal pentact series. 

 This may be presumed by comparing the young basalia or pleuralia with the adjacent 

 hypodermalia, but the fact is distinctly demonsti'ated by studying sections of young, 

 spherical or oval specimens, 2 to 5 mm. in diameter (PL LIII. figs, la, h) (probably 

 developed from ova), which were found in the same glasses as the Hexactinellids from 

 Station 192, Little Ki Island. At the lower, often somewhat truncate pole, opposite the 

 oscular aperture, between the ordinary hypodermal pentacts, other forms occur in which 

 the four tangential rays do indeed lie in the dermal membrane, but are bent more 

 markedly inwards than the others, and are beginning to resemble the anchor-teeth of the 



