56 T. IJIMA : HEXACTINELLIDA. I. 



verge of developing into a discohexaster as like a discohexaster 

 just before losing the last vestige of the terminal armature. Never- 

 theless, T believe that discohexasters in the broad sense are all to bo 

 regarded as having been derived from oxyhexasters by complica- 

 tion of parts. I say this not on purely a priori grounds alone 

 but also from the nature and mode of the growth of hexaster- 

 terminals in general. Concerning the oxyhexaster of Eiqjiectella 

 in particular or of the onychaster of any genus, I have made 

 none or but little direct observation as to the development of the 

 terminals. However, in certain Rossellid species I have not 

 infrequently met with unusually small oxyhexasters of typical 

 shapes, in which the terminals were presumably still growing. 

 How these grow in the floricome (a discohexaster) and the 

 graphiocome (an oxyhexaster), has already been referred to in brief 

 and will be described in greater details under E. marshalli. 

 These observations seem to sufficiently warrant the induction that 

 the hexaster-terminals are in all cases secondary appendages at 

 the outer end of the principals, or primary rays which alone 

 inclose the axial filament, — local formations which at their inci- 

 pient stage are exactly comparable to the simple microtubercles 

 or spines that so frequently beset the spicular surface. It appears 

 then assuraable that the discohexaster-terminals originally ended 

 in simple points as the oxyhexaster-terminals always do and that 

 the terminal disc or whorl of claw-like processes is, so to speak, 

 a tertiary structure added to the simple end of the terminals after 

 these had grown to their full length, — a factual demonstration of 

 which changes is found in the development of the floricome. 

 Thus the ontogenetic and phylogenetic sequence of discohexasters 

 to oxyhexasters in general seems to be plain, and the onycho- 

 oxyhexaster probably represents a stage of the passage of the 



