THE C03IM0N FKESH-WATER SPONGE. 
7 
the common sponge cells, polymorphic. But the chief interest of 
these masses was connected with their investing covering, which 
consisted of a layer of firmly cohering cell-like globules. Some 
of the latter were also like the common sponge-cells, being 
granular and nucleated ; but others enclosed amphidiscs in 
various stages of development. The most rudimentary of these 
spicula only appeared like slender rods slightly thickened at each 
extremity ; in a second form these rods had very delicate setcB 
radiating from and arranged at right angles with their thickened 
ends. Thus the amphidiscs, as we have already shown from 
Carter’s observations to be the case with the pointed spicula, 
begin to exist as slender rods, which become thickened by 
additions to their external surfaces ; both the spicula and the 
amphidiscs being formed in the interiors of sarcoids, or proto- 
plasmic sponge-cells. 
Besides the reproduction by gemmules, already described, 
various indications have been seen sugo^estive of other modes in 
which the species is multiplied ; but considerable doubt attaches 
to many of these, from the circumstance that various infusorial 
animalcules find their way into the sarcode of Spongilla, which 
may readily be mistaken for essential parts of the organism. 
Both Carter and Lieberkuhn recognise numerous groups of 
germ-cells in the parenchyma, the contents of which become de- 
veloped into sponge-cells. Lieberkuhn terms these groups germ- 
granules ; but the latter observer has seen in addition what he 
terms ‘‘swarm-spores.” On leaving recent sponges for some hours 
in water he observed free atoms moving about having a length 
of about 3L- and a width of of an inch at their broadest part. 
These objects swam about freely for one or two days, and then 
sank to the bottom of the water, where they underwent a further 
development. Each one soon expanded into a structureless mass, 
containing fine siliceous needles. On the 20th day the mass had 
not only become larger but contained all the constituent ele- 
ments of young sponges — ^viz., smooth and muricated spicules, 
polymorphic cells, large and small granules, some germ-granules, 
and external cilia effecting locomotion. Lieberkuhn thought 
that the cilia were attached to a single epithelial layer of con- 
tiguous, but not mutually compressed, cells, each cell having a 
single cilium. These observations, taken along with others 
already referred to, demonstrate the strong tendency existing in 
spongilla to the development and liberation of mono-ciliated 
sarcoids or sponge-cells. Each swarm-spore developed into an 
organism having a structureless (?), gelatinous cortical portion 
and a more distinctly organised medullary mass. Lieberkuhn’s 
detailed descriptions of the appearances presented by these struc- 
tures, in the course of their development, differ widely from those 
noticed by Carter in the products of the brown gemmules ; but in 
