304 E. A. MINCHIN. 
ments to some extent; the full-grown triradiates, placed more 
towards the dermal surface, can be seen plainly to bulge out 
the dermal surface so as to produce depressed areas in the 
angles between the rays, in all Ascons (compare fig. 71 0). 
Unfortunately for Woodland’s theory, however, this only 
applies to the full-grown spicules; the young triradiates 
develop far in, close to the gastral surface, where the super- 
ficial depressions do not reach, and where consequently no 
erooves can direct the apical cells in their untutored wander- 
ings.! 
IX. GeneRAL Remarks ON THE FORMATION OF CALCAREOUS 
SPICULES. 
A spicule may be defined briefly as a sclerite, or skeletal 
element, of intra-cellular origin. The chief interest which 
1 I must point out that Woodland has occasionally fallen into some 
errors of statement in relation to objects which he has not himself studied. 
In one place (1905, pp. 238, 239, foot-note) he speaks of tuning-fork 
spicules in the stalk of Clathrina lacunosa. It is hardiy necessary for 
me to point out that no such spicules occur in this sponge; Woodland was 
apparently thinking of the elbowed monaxons of the stalk, spicules of a very 
different type. Tuning-fork spicules are characteristic of the extinct Phare- 
tronide and of some recent heteroccelous genera, such as Lelapia, probably 
allied to the Pharetrones; they are not known in any Ascon; and their 
position in the body of those sponges which possess them does not at all con- 
firm Woodland’s explanation of their form and characters. In another place 
(l.c., p. 274) Woodland states that ‘“‘in no calcareous sponges do there co- 
exist small monaxons . . . . with triradiates,’’? but that either small 
and large monaxons, or large alone, are found. Now, the common Leuco- 
solenia botryoides of our coasts, the earliest described species of Ascon, 
always has triradiates in great abundance, some of them very thick and 
massive; but its monaxons are frequently so small that they have been com- 
pletely overlooked by spongiologists of repute, and require high powers to find 
them (compare Minchin, 1905 [2], text-fig. 97, p. 388). [Since this was 
written Woodland has corrected his statements concerning Clathrina 
lacunosa (1908, p. 148, footnote). ] 
Lapses of this kind are like the proverbial flies in the ointment; they 
weaken the theoretical conclusions which they are adduced to support, and 
they are a joy to the hostile critic. Woodland has himself produced such an 
abundant crop of valuable data upon spicule-formation that it is to be regretted 
that he did not rely more upon his own material as a basis for his speculations. 
