/)0 I. IJIMA : HEXACTINELLIDA. I. 



which is either open or closed by the bottom-plate. The sponge 

 throughout life is constantly regenerating and projecting new 

 anchoring spicules ; hence, young specimens of the same of vari- 

 ous lensfths are always to be found in abundance with head and 

 shaft still contained in the bundles within the parietes. With 

 the continued elongation of the shaft, which takes place parti- 

 cularly in the proximal ray, they are protruded downwards, the 

 head-end first, to be driven further and further into the sub- 

 stratum. 



Exceptionally, the barbed basalia may be monactins brought 

 about simply by the entire obliteration of the distal ra}^, thus 

 bringing the axial cross to a position within the anchor-head. 

 Such a modification seems to exist in E. cr assis tellata F. E. Sen. 

 ('87, p. 82) and also in Placopegma solutum F. E. Sen., a peculiar 

 form which is not without affinity to the Euplectellidœ. For 

 the latter species F. E. SenuLZE ('95, p. Q>5) has expressly stated 

 that the anchor-teeth, four in number to each head, are to be 

 considered not as secondary spines but as real rays, — a view 

 which is not acceptable, since the transverse axial canals as 

 plainly shown in his figure are very short and far from extend- 

 ing even to the base of the teeth. 



On the other hand, an essentially different type of anchoring 

 spicules — genuine pentactin anchors — has been discovered by 

 F. E. SenuLZE as occasionally present, in addition to the barbed 

 diactin type, in the root-tuft of certain Euplectella species (E. 

 aspergillum, simplex, asper). The unpaired ray is prolonged into 

 the shaft which is perfectly smooth, while the short cruciately 

 disposed rays at the inferior end are recurved and form the 

 anchor- tee til. The latter are each traversed throughout by the 

 axial canal. 



