70 Journal of the Asiatic Society of Bengal. (January, 1913. 
The pore-cells in N. mappa are highly specialized (plate 
area varying from about 12 to about 20. The orifices vary in 
diameter from 0°045 to 0°0675 mm. They are naturally circular 
but in mounted preparations are liable to distortion. Each 
pore-cell consists of a slender ring of cytoplasm which stains a 
little darker than that of the ordinary flattened epithelial cells 
and has an obscurely reticulate structure. The nucleus is ellip- 
tical in form, measuring about 0:006 x 0-003 mm., the greater 
axis lying parallel to the circumference of the aperture, on 
which the cell encroaches in the form of a slight bulge opposite 
the nucleus. So far as I have been able to discover there is no 
break in the continuity of the ring formed by the pore-cell. 
In specimens of the sponge that have been dried after 
careful preservation in a liquid medium (plate v, fig. 2) the 
to stand out in sharp contrast to the imperforate roof of the 
branching exhalent grooves. In part of the type of NV. reversa 
(plate v, fig. 3) which I have dried there is a comparatively 
large area of perforate membrane, but it is not confined to the 
orifices of the inhalent channels or defined in any exact manner. 
either in N. reversa, N. aster or Cortispongilla barroisi. The 
mechanical difficulties involved in a careful examination of the 
lermal membrane in the two last species are, however, con- 
siderable. 
so readily, are more difficult to detect. They resemble those of 
N. mappa in structure but are smaller, the aperture of the 
largest pores having a diameter of about 0-02 mm. 
My specimens of N. mappa and E. fluviatilis syriaca were 
scraped from stones with a knife before being preserved, but 
notwithstanding this violent treatment, their pore-cells appear 
upon the cover and rotated until the glass is broken and the section 
completely crushed. The fragments of glass and all but the smallest 
fragments of sponge are then removed with a pair of fine forceps and 4 
new cover-glass is put on. 
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