278 W. WOODLAND. 
adult organism in order to there produce, or aid to produce, 
a spicule of a particular conformation; i.e. it seems impos- 
sible to attribute the production of these secondary forms of 
triradiates to inheritance. The direct action of the environ- 
ment in determining the disposition of spicules is particularly 
well shown in the Leucosolenia diverticula mentioned 
above, where, owing to a change in the architecture of the 
sponge body, and in consequence to a different mode of 
action of the environmental forces, the disposition of the 
triradiates immediately becomes altered. 
Prof. Minchin, to whom I am indebted for so many of my 
facts, has, in the paper before referred to, put forward an 
ingenuous hypothesis respecting the evolution of triradiate 
spicules, contending that such have arisen, through natural 
selection, by the apposition and fusion of primitively sepa- 
rate monaxons, their extremities being brought together by 
the agency of pore-distribution. And a somewhat similar 
idea has previously been expressed by Schulze, who, after 
asserting that “in the angle between any two rays (of the 
triradiates) a pore is situated” (which is only true to a 
certain extent for some Clathrinidee—in all other calcareous 
sponges no such relationship between the pores and the 
triradiates being observable at any stage of growth), con- 
tends that the equiangularity of the triradiate is “to be 
explained in much the same manner as in the honeycomb.” 
I exceedingly regret having to differ from high authority 
on these matters, but, for the present, | must adhere to my 
own explanations, if only for the reason that they present 
to my mind more definite conceptions of the causes involved. 
I think it highly improbable that survival of the fittest can 
have had much to do either with the modes of disposition or 
with the primary or secondary forms which the spicules 
assume. 
