192 LIEBERKUHN, ON MOTILE 
brane enlarged in such a manner and to such a degree that 
at last nothing but a network of filaments remained, exactly 
like that constituting the internal parenchyma, with which, in 
the course of the day, it became so united that the whole struc- 
ture completely lost the usual appearance of a sponge, since 
even the exhalent eanal had disappeared. In this condition 
the sponge resembled a gigantic Rhizopod lodged in a siliceous 
skeleton. Even with the naked eye the stronger filaments 
might be seen, constituting a network of whitish filaments 
within the skeleton. . These, however, did not long retain 
their form, but became thicker or slenderer in the most 
various degrees ; but so slowly, nevertheless, that the change 
could not be directly witnessed, though its reality could be 
concluded upon from the alteration in form. In the interior 
of some of the trabeculz were enclosed large balls of detritus, 
but whence derived could not usually be determined ; in only 
a few cases could the author recognise in them traces of 
decomposed cells of Alge. The cells of the outer membrane 
precisely resemble those of the internal parenchyma; in the 
state of contraction above described they coalesce as readily 
with the latter as those do with each other. It appears, even 
in Spongille which have originated in detached portions, that 
the external membrane may be formed in a few hours from 
the cells of any part of the tissue. Nor are the inhalent 
orifices by any means characteristic of the outer membrane, 
since orifices of exactly the same kind may be observed in 
the internal membraniform septa. Besides this, in the so- 
termed process of “conjugation” the cells of the outer 
membrane unite, not only with the same cells of the other 
individual, but equally well with those of the rest of the 
parenchyma. 
Very remarkable are the changes of place witnessed in 
the individual cells in the transparent exhalent passages. 
The latter, especially in their deeper parts, frequently consist 
of several layers of cells; the outermost of these layers is a 
continuation of the outer membrane of the sponge, whilst the 
inner ones are continuous with the rest of the parenchymatous 
tissue. These cells may occasionally be seen, whilst under- 
going a continual change of form, to move slowly upwards 
and downwards. Sometimes, also, an individual cell may be 
seen to penetrate between two which retain their position, 
and ‘afterwards follow the other, whilst the form of the canal 
retains its general form unaltered. In some points of the outer 
membrane globular or conical protrusions not unfrequently 
arise, which acquire the diameter and length of exhalent 
tubes, and which may become annularly constricted, and 
