MATERIALS FOR A MONOGRAPH OF THE ASCONS. 349 
1907 (2). Wooptann, W.—“ A Preliminary Consideration as to the Possible 
Factors concerned in the Production of the various Forms of 
Spicules,” ‘Quart. Journ. Mier. Sci.’ (N.S.), vol. 51, pp. 55—79. 
“Studies in Spicule Formation. VIII. Some Observations 
on the Scleroblastic Development of Hexactinellid and other Sili- 
ceous Sponge Spicules,” ‘Quart. Journ. Mier. Sci.’ (N.S.), vol. 52, 
pp- 139—157, pl. 7. 
1908 (1). 
EXPLANATION OF PLATES 17—21, 
Illustrating Mr. H. A. Minchin’s paper on “ Materials for a 
Monograph of the Ascons.” 
On Plates 17—20 all the figures, except Fig. 101 on Plate 20, are drawn to a 
magnification of 1000 linear. 
PLATE 17. 
Vigs. 1—$.—Development of the small straight monaxons of 
Leucosolenia complicata, as seen in surface views of the wall 
of the sponge. 
Fic. 1.—Scleroblast with two nuclei and commencing separation of the two 
formative cells. No trace as yet of spicule-formation. 
Fre. 2.—Similar stage, but with the first foundation of the spicule indicated 
as a delicate line, passing obliquely between the two nuclei. 
Fig. 3.—The delicate line of the last stage has expanded into a clear, fusi- 
form area, sharply limited from the surrounding cytoplasm. No trace as yet 
_ of mineral deposit. 
Fic. 4.—Similar stage to the last; the clear space is larger, and running 
through part of it a delicate axial line could be made out. 
Fic. 5.—Commencement of mineral spicular deposit within the clear space, 
which it far from fills. 
Fic. 6.—A later stage; the “‘ thickener” beginning to travel away from the 
projecting distal extremity of the spicule. 
Fic. 7.—Spicule nearly fully formed; the thickener quite close to the 
founder. 
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