314 W. WOODLAND. 
inferred that a geometrical, i.e. crystalline, structure is 
interposed between two stages of spicule growth which are 
non-crystalline in form—the spherical granule and the adult 
triradiate. This is evidently grossly improbable 4 priori. 
There is nothing very objectionable in commencing with a 
crystal as a nucleus for the future spicule, but to interpose 
one in an otherwise uniform series of non-crystalline meta- 
morphoses is a proceeding to be regretted; and (2) because 
of the rarity of the occasions on which this tetrahedron is 
stated to have been observed. For these two reasons, then, 
I think it more feasible to suppose that the observers named 
TExt-Fic. 7. 
A B 
mistook the small three-cornered mass which represents the 
transition from the spherical granule to the young triradiate 
calcareous spicule. For certain reasons I do not think this to be the case. 
Firstly, it may be remembered that before the formation of the tetrahedron 
takes place there are several cells heaped together in Echinocyamus, each 
with one or more calcareous granules of uncertain shape. Now it seems 
rather singular that only one of these granules should be 
transformed into a tetrahedron, while the remaining ones are pro- 
bably dissolved, and by successive depositions give rise to the further increase 
of the calcareous body. Besides, it is common to all calciferous cells to 
possess such granules.” (The italics are mine.) The further description 
and figures given below of what occurs in Echinus esculentus offer a 
sufficient answer to this argument of Théel, who evidently had not observed 
the phenomena I have described. 
