BY R. VON LEXDENFELD, PH.D. 1101 



directed basal ray to the zone of the cortical acerate spicules. 

 Tuber Acerate lying pai-allel to the basal ray just mentioned, and 

 tubar quadriradiate spicules scattered here and thereat the bottom 

 of the radial tubes. 



Subgastric triradiate Spicules : All rays of the same thickness, 

 0"013 mm ; basal ray straight, tapering from the base to a sharp 

 point, its average length 0*3 mm. ; lateral rays slightly curved 

 inwards, forming with basal ray an angle varying from 100 c> to 

 110°, rarely exceeding 015 mm. in length. 



Tubar quadriradiate Spicides : All rays in different planes, 

 lateral rays forming one curve, basal and apical rays another ; 

 basal ray bluntly pointed, cylindrical 0-0025 mm. thick, rarely 

 longer than 0*003 mm. ; lateral rays straight or slightly curved, 

 tapering from the base to sharp points, each forming with basal 

 ray an angle of about 110°, reaching 0-05 mm. in length, with a 

 diameter of 0-002 ; apical ray slightly curved, sharp pointed, of 

 the same diameter as lateral rays, but usually three times shorter. 



Tubar acerate Spicides : Straight or slightly curved, tapering 

 from the centre to sharp points, l'arely longer than 0*3 mm., with 

 a diameter of 0-005. 



Skeleton of the Cortex : The skeleton of the Cortex consists of 

 large spindle-shaped acerate, of minute acerate, and of sagittal 

 triradiate spicules, with the basal ray directed towards the closed 

 end of the Sponge. 



Large acerate sjricides straight or slightly curved, tapering from 

 the centre to a sharp point at either end ; length varying from 1 

 to 3 mm., diameter from 0*05 to 0-12 mm. 



Minute acerate Sjncules : Like those of the gastric surface 

 spindle-shaped, straight, or slightly curved, tapering from the 

 centre to sharp points, rarely exeeding 0-15 mm. in length and 

 0-0028 mm. in diameter. 



Sagittal triradiate Spicides ; Basal ray smooth, either of 

 cylindrical form or tapering from the base to a sharp point, 

 reaching 0*75 mm. in length, with a diameter of 0-005 ; lateral 

 rays sharp pointed, forming with basal ray an angle of 112°, 



