A SIEVE-LIKE MEMBRANE IN LEUCOSOLENIA. 271 
EXPLANATION OF PLATES X and XI. 
Illustrating Mr. Edward A. Minchin’s “ Note on a Sieve-like 
Membrane across the Oscula of a Species of Leucosolenia, 
with some Observations on the Histology of the Sponge.” 
ect. Ectoderm. ezd. Collared endoderm. s.m. Sieve membrane. G. c. 
Gastral cavity. p. Pores. 2. Nuclei. sp. sh. spicule sheath. 
PLATE X. 
Fic. 1.—Vertical section of an oscular tube. Osmic and hematoxylin. 
Zeiss, oc. 2, obj. B. 
Fic. 2.—Vertical section of an osculum which has just divided into two. 
Osmic, picro-carmine, and hematoxylin. Zeiss, oc. 4, obj. D. 152. 
Fic. 3.—Vertical section of a small oscular tube, in which the sieve mem- 
brane was without any opening. ‘There are no pores to be seen in the walls 
of the tube, and the collars of the endoderm-cells are very low. Osmic, 
picro-carmine, and hematoxylin. Zeiss, oc. 4, obj. D. 24°. 
Fic. 4.—Collar-cells from another part of the same section as Fig. 3, to 
show the normal height of the collars relatively to the cells. Zeiss, oc. 8, 
obj. F, apochrom. 285, 
Fic, 5.—Side view of an oscular tube, seen as a transparent object. Osmic 
half per cent., acetic acid half per cent., glycerine. Zeiss, oc. 2, obj. B. 
Fic. 6.—A portion of the sicve membrane of the osculum drawn in Fig. 5, 
dissected out. Zeiss, oc. 8, obj. F, apochrom. +22, 
Fic. 7.—A_ portion of the wall of the oscular tube above the sieve mem- 
brane, from the osculum drawn in Fig. 5. Zeiss, oc. 8, obj. F, apochrom. 
Fic, 8.—A portion of the wall of the sponge from below the sieve membrane. 
From the osculum drawn in Fig. 5. The spicule sheaths are barely visible on 
account of the opacity of the preparation. Zeiss, oc. 8, obj. F, apochrom. 
Fic. 9.—Portions of the sieve membrane of an osculum, dissected out to 
show the nuclei in the nodes. Osmic half per cent., picro-carmine, glycerine. 
Zeiss, oc. 8, obj. F, apochrom. 
Fic. 10.—View of an osculum looked at from above, showing the sieve 
membrane, partly hidden by the edge of the aperture, stretched out over the 
oscular opening. Absolute alcohol, hematoxylin. Zeiss, oc. 2, obj. B. 22. 
Fic. 10¢.—The whole of the sieve membrane of the same specimen. Zeiss 
oc. 4, obj. C. 
