572 E. A. MINCHIN. 



seemed likely to yield interesting results, since it is a form in 

 which the rays unite at a very early period (see Addendum B, 

 infra). The preparation showed clearly filaments in the mon- 

 axons and in the gastral rays, but with regard to the latter I 

 was not able to make out clearly in surface view their relations 

 to the filaments in the basal triradiate system. In the tri- 

 radiates which I examined I could only find one instance 

 showing a distinct, but small, central triangle. In all the 

 other cases the filaments appeared to meet at the centre, but 

 closer observation showed that they were united by, or were in 

 contact with, a distinct central granule which stained a little 

 more deeply than the contiguous ends of the filaments. I 

 think this observation, so far as it goes, confirms my view of 

 the significance of the central triangle. 



In any case I think these observations afford the most con- 

 clusive proof of the existence of an organic axial filament in 

 the calcareous sponge spicule. Haeckel (1872) and SoUas 

 (1885) affirmed the existence of this structure, while Ebner 

 (1887) denied it. Lendenfeld (1885) gave a most detailed and 

 circumstantial description of the axial filaments (see above, 

 p. 538), but I find it difficult to believe that he saw anything 

 of what he described ; for when Ebner cast doubts upon the 

 existence of an organic axis to the spicule, Lendenfeld in his 

 very next paper on the subject (1891, p. 382) acquiesced in all 

 Ebner^s statements without a protest, not even so much as 

 mentioning that he or any one else had ever described such a 

 structure. 



B. On Compound Spicular Systems behaving as 



Single Crystals. 



(Note to p. 557.) 



With regard to the apparent paradox which is presented by 

 the triradiate and quadriradiate spicules, namely, the fact that 

 while on the one hand they are bodies of multiple origin, they 

 behave on the other hand as single crystals, I am indebted 



