2 
POPULAK SCIENCE REVIEW. 
of these experienced observers, our acquaintance with the Spon- 
gilla has assumed a much more definite and correct character. 
Most naturalists now admit its animal nature, whilst they recog- 
nise fully its many points of close afl&nity to the lowest plants. 
Its position in the scale of organised forms is near the base of 
the organic pile, where plants and animals present so many 
points in common that the most skilled students have ever been 
at a loss to define the boundary line between the two kingdoms. 
Speaking scientifically, Spongilla is a rhizopodous animal, be- 
longing to the same class as the sponges, foraminifera, polygastric 
infusoria, and their various allies. 
There are probably few parts of the world where it may not 
be found. It is common in the ponds of our own country, as 
well as in various parts of Europe. Carter found it in the tanks 
of Bombay ; and, like many other low types of organization, it 
has doubtless a cosmopolitan range. The finest specimens I ever 
obtained were from the huge posts supporting some of the gates 
of the London Docks. 
When small specimens are met with they appear as slimy, 
roundish masses (fig. 1), not unlike many of the gelatinous 
fresh-water Algae ; but as they advance in growth they assume 
various forms, partly dependent upon the situations in which 
they live. They usually occur as irregular masses, clustering 
round the object to which they attach themselves, presenting 
slight appearances of projecting lobes and ridges. Occasionally 
they become slender branching objects, from six inches to afoot 
in length — a type more frequently seen in running streams than 
in stagnant waters. 
The unaided vision readily detects three distinct elements 
in the organisation of Spongilla : the investing jelly, or sarcode; 
an internal skeleton of harder and brittle material (fig, 2a), and 
multitudes of small yellowish seed-like bodies (fig. 26), espe- 
cially abundant towards the central and lower parts of the or- 
ganism. When removed from the water and dried the sarcode 
almost disappears, leaving a very brittle mass (fig. 2), which the 
slightest pressure reduces to fragments. A low microscopic 
power demonstrates that this friable structure is an aggregation, 
of siliceous spicula and round seed-like bodies, cemented together 
by the dried up sarcode. 
In endeavouring to record the chief points that have been as- 
certained respecting the minute history of Spongilla, we are met 
by the difficulty that though many have written about it, its real 
observers h ave been few in number and recent in time. This would 
constitute no difficulty if the few were agreed; but in some im- 
portant details this is not the case. Such discrepancies amongst 
the historians of the lower plants and animals often arise from 
the fact that these organisms have many-sided histories; and it 
