lo,S ART. 7. — I. TJIMA : TTEXACTINELLTDA , IV. 



their formation by a coalescence of parts rnnning lengthwise. If 

 more support is needed to establish the correctness of F. E. 

 Schulze's enunciation as to the nature of the discoctaster, a note- 

 worthy fact may be adduced with respect to the typical triaxial cross 

 of filaments inclosed in the central node, which I believe I was 

 the first to demonstrate in the spicule under consideration ('97). 

 As I have repeatedly had occasion to remark, the cross becomes 

 plainly visible if the spicule be examined in glycerine or in any 

 otlier medium of a refractive power similar to that of the siliceous 

 substance, and its six points are seen to be always directed towards 

 the middle of the space surrounded by every set of four secondary 

 principals. That space is either simple-surfaced and somewhat 

 concave or shows in the middle the hump-like protuberance before 

 alluded to. In the latter case, each arm of the axial cross extends 

 directly into the protuberance towards which it is directed (see 

 PI. XI., fig. 20). Of some interest is the not infrequent occurrence 

 of malformed discoctasters in which there exist such a primary 

 t 'rminal or terminals as stand out from the central node, having 

 apparently been left fi-ee without fusing with any of the secondary 

 principals (PI. XIIL, fig. -3; PI. XVI., fig. 10; PI. XVIIL, fig. 

 T) ; etc.). The cases may be said to be in a measure suggestive 

 of the condition of the spicule before the primary terminals were 

 brought together and joined into the eight secondary tufts. 

 Noteworthy also seems the presence of minute vacuole-like spaces 

 in the secondary princi})als and sometimes also in the central 

 ]iode (PL XIL, figs. 2.",, 27 ; PI XV., fig. 1) ; etc.). In the 

 former as well as in the ridges running out from the six pro- 

 tuberances on the central node, the little spaces are usually found 

 arranged in a row or rows that run longitudinally. There can 

 scarcely be a doubt as to their being vacancies between the 



