STUDIES IN SPICULE FORMATION. 319 
deposit calcareous salts in a liquid state in the common 
pseudopodial clump, where the formation of the tetrahedron 
afterwards takes place . . . The minute tetrahedron grows 
rapidly to a small star with three very short arms, acquiring 
a shape almost completely corresponding to the interspace 
between these [three] close-lying calciferous cells. Thus one 
is almost tempted to think that there exists a certain relation 
between the form of the deposit and the interspace in question. 
The calciferous cells having placed themselves close to the 
ectoderm, the deposit becomes pressed between them and the 
latter. If it be so, that this interspace decides the outline 
of the star, one would expect always to find it in its early 
developmental stage placed just between the calciferous cells. 
This seems, however, rarely to be the case. Mostly I have 
noticed the star situated by the interspace with the arms 
upon the three cells and not between them, and sometimes I 
have seen the star itself somewhat displaced. Notwithstanding 
this, I cannot free myself from the thought that the cells 
mechanically exercise influence on the outline of the tetrahe- 
dron, and the star in the earliest stages of the development.” 
_ There yet remains, of course, a third possible supposition, 
viz. that the form of the triradiate spicule is due to some 
agency at present unknown, as e. g. that complex of physical 
causes termed heredity, but since this supposition certainly 
does not constitute an explanation—does not affiliate the 
phenomenon under discussion to other phenomena whose 
mode of production is known—I am not prepared to discuss 
it. 
FurtHER GROWTH OF THE 'I'RIRADIATE SPICULES, ETC. 
To proceed once more with the description. Though, in 
BE. esculentus, the skeleton of the larva primarily originates 
in two centres—the two triradiates of the longitudinal strands 
—yet it often happens that isolated granules, rods, and 
(occasionally) triradiates arise independently in other regions 
