MATERIALS FOR A MONOGRAPH OF THE ASCONS. 577 



the fact, at first puzzling, that a compound spicular system 

 behaves as a single crystal. 



These speculations are impossible to test, unfortunately, 

 unless by some happy chance an Ascon or calcareous sponge 

 should be found in which monaxon spicules, laid down and 

 built up separately, are joined together after attaining their 

 full growth, to form triradiate systems. But it would be 

 interesting to examine between nicols the compound masses 

 formed by fusion of spicules in such a form as Petrostoma 

 (Doderlein, 1897), in order to see whether the masses in 

 question behave as single crystals or show a number of crystal- 

 line centres corresponding to the number of spicules which 

 have been united. 



As regards the significance, from the point of view of crystal- 

 lography, of the fact that the spicules at their first appearance 

 are not crystalline, I think I had better leave the explanation 

 to those who are more conversant with the facts and theories of 

 crystallisation than myself. I may, however, point out that 

 since an organic axis to the spicule ray has now been demon- 

 strated, it is evident that the greater part of the spicule ray at 

 its first appearance would be organic in its composition ; a 

 fact which may perhaps furnish a clue to the mystery — if there 

 be a mystery. 



S u m m a ry of Addendum B . 



(1) The rays are non-crystalline so long as they are distinct 

 from one another. 



(2) They may remain non-crystalline for some time after 

 union has taken place. 



(3) The crystallisation appears to start from the secondary 

 deposit which unites the rays at the centre. 



(4) With regard to the period at which the rays become 

 crystalline, the species con tort a, cerebrum, falcata, and 

 reticulum form a diminishing series, the last-named being 

 the species in which crystallisation sets in earliest. 



(5) Those triradiate systems which, by hypertrophy of two 



