STUDIES IN SPICULE FORMATION. 281 
may be its nature) causing division of the scleroblasts 
initially concerned in the production of the monaxon. 
Again, it is obviously probable 4 priori (as mentioned in 
the text) that if three scleroblasts associate, two also should 
associate, and in this latter case there will, under the 
conditions, inevitably result a monaxon structure. But if 
monaxons can either be produced from a single binucleated 
scleroblast or from an association of two scleroblasts, then, 
since in the latter case the initial capital is twice as great as 
that in the former, a difference in the size of the two classes 
of monaxons might be anticipated. This is the case in the 
Sycons, as text-fig. 1 shows. Although, of course, there 
exists a certain range of variation in size in each type of 
spicule, yet the thin and the thick monaxons are tolerably 
distinct from each other. 
EXPLANATION OF PLATES 13—15, 
Illustrating Mr. Woodland’s paper, “Studies in Spicule 
Formation.” I. 
All figures magnified 1000 diameters and drawn with camera lucida. 
PLATE 13. 
Fic. 1.—Two ordinary scleroblasts. 
Fie. 2.—The same with the nucleus enlarged. 
Fic. 3.—Division of the scleroblast nucleus; in a the binucleated condition 
has probably been produced by an association of two cells, and not by a 
division of one; in c the cell-substance is more elongated than usual. 
Fic. 4 shows the pale streak or “‘ mould” in the cytoplasm. 
Fies. 5—12 illustrate the further development of the monaxon spicule. 
Fig. 7, 4, is slightly abnormal in its shape. The white streak is also seen in 
Figs. 11, 4 and e. 
Fic. 13.—Groups of three scleroblasts in S. coronata probably about to 
associate to form the trefoil. 
Fic. 14.—The trefoil stage. 
Fic. 15.—Division of one of the trefoil cells—first stage in formation of 
sextet, 
