MATERIALS FOR A MONOGRAPH OF THE ASCONS. 301 
Materials for a Monograph of the Ascons. 
II.—The Formation of Spicules in the Genus Leucosolenia, 
with some Notes on the Histology of the Sponges. 
By 
E. A. Minchin, Wi.A., 
Professor of Protozoology in the University of London, 
With Plates 17—21, and 5 Text-figures. 
Contents. 
. PAGE 
I. Introductory . ‘ : ; 5. (ao 
II. The Monaxon Spicules_ . : : . 9305 
III. The Triradiate Systems . i : Eola 
IV. The Gastral Rays : , 5 Bly 
V. Derelict Spicules in Taweccslouts complicata 5 oil 
VI. Histological Notes ; the Excretory Cells of Leucoso- 
lenia complicata . 5 ‘ . 322 
VIL. An Abnormal Triradiate . : 327 
VIII. Some Observations on the Disposition of the Girreaiate 
Systems of Leucosolenia lieberktthnii oot 
IX. General Remarks on the Formation of Calcareous Spic- 
ules : : . ; . dd4 
Bibliography . : : . 347 
Description of the Blates! ; : . 349 
I. Inrropucrory. 
In former memoirs (1896, 1898, 1905 [1]) I have proposed 
to divide the Ascons, or Calcarea Homoccela, into two 
families, Clathrinide and Leucosoleniide, differing 
VOL. 52, PART 5.—NEW SERIES. 24 
