INFUSORIA. 17 
difficult to classify them properly. They are principally made up of 
irregular, globular, fan-shaped, palmate, branched, cup-shaped, funnel-shaped 
(often of great size), tubular, leaf-shaped, or ragged forms, which either 
surround other objects, or rise upon a short pedicle. The cup-shaped 
S. usitatissima, and the trumpet-shaped S. tubeformis, are from the 
American seas. The former is an article of commerce. S. jistularcs (pl. 
75, jig. 44) is a large brown species, with fine and very flexible fibres, from 
the American seas. 
Notwithstanding the investigations of zealous inquirers, polyps have not 
been found in sponges. A number of observers who have watched their 
growth from the commencement, first observed the gelatinous substance, 
and afterwards the filamentous matter in it, which may be regarded as a 
skeleton. The growth of sponges is quite different from that of corals, as 
might be expected from the absence of polyps. Some regard the circulation 
of water through sponges as a kind of breathing process, a view which is 
inadmissible. With respect to their propagation, but little is satisfactorily 
known. According to Olivi, small oval bodies are found in the jelly-like 
mass, especially in autumn, which have been too hastily named eggs. 
Sponges contain calcareous or silicious spicula, in which they resemble 
certain plants. They may be detected by burning a piece of sponge and 
placing some of the ashes beneath a microscope. These spicula are 
uniform in each species; so that they are useful in affording specific 
characters. 
The chief peculiarities of marine sponges are also found in the fresh 
water species, as Spongille lacustris; S. fluviatilis; and S. friabilis, 
which inhabit swamps and running streams. The three named species, 
however, constitute probably but one, at different stages of growth. 
The following genera are placed here, because, according to Milne 
Edwards, they have no polyps (new edition of Lamarck, vol. 2, p. 208, 
520, 522). Some of the best authorities place them among plants. 
Penecillus penecillus, Linn. (pl. 75, fig. 37), resembles a hair pencil, and 
the stem has a whitish calcareous crust (American seas). Jabellaria 
opuntia, Linn. (fig. 36) (American seas). Acetabulum mediterraneum ( jig. 
41). Corallina officinalis, Linn. (pl. 75, jig. 38), white, reddish, or green, 
four inches long. C. rubens (jig. 35) (Mediterranean). These delicate 
bodies were long supposed to partake of the animal nature of the true 
corals ; but the structure is now considered to be nearer that of the alge. 
Pedicellarra, Miller (pl. 75, fig. 4), is a portion of an Echinus. 
Crass InFusoriA. 
These minute animals have been observed and studied only since the 
discovery and improvement of the microscope. Several species were 
known in ancient times, because they occurred in such numbers as to 
discolor the water green or red, in the latter case giving it the appearance 
221 
