



SPONGES. 305 
feculent matter through the larger openings. The meshes 
of the sieve and the channels are thickly lined with myriads 
of microscopical animalcule, to which the perpetual current 
bears their minute food, sifted of all the coarse, unsuitable 
particles, and maintains an invigorating supply of fresh sea- 
water throughout the whole colony. The animals themselves 
create this current by the motion of ciliæ, or little hairs, 
which grow out from the region of the mouth. The form of 
their bodies has been ascertained in only one species, called 
Leucosolenia botryoides. In this, which is quite small, 
though common on the shore, Professor H. J. Clark found 
that they were minute sac-shaped beings, with a collar pro- 
jecting from the free end, in the middle of which was the 
mouth, situated at the base of a long filament which was 
hardly ever at rest. It seemed to be employed principally 
m casting morsels of food down into the mouth, and this 
action, in itself so slight, is yet, when carried on by the thou- 
sands of neighboring filaments, sufficient to keep the fluids 
n rapid motion through the meshes. 
Until of late years the animal nature of the sponge was 
disputed. Then it was referred to the Ameba forms, crea- 
tures which are mere sprawling drops of jelly, without 
mouths or stomachs, but which, however, manage to move 
Wout, and even in some species build up most elaborate 
internal structures resembling minute shells. Now, through 
the investigations of Professor H. J. Clark, we know that 
they are colonies of such comparatively highly organized 
beings as those I have described, and we are ulso able to 
State, upon the same authority, that their young are. free, 
roving globules, resembling an isolated individual of the 
parent stock, 
The mode of growth has not been studied in the sponge 
itself, but in a closely allied animal where a number of lit- 
tle bells grow upon a stem (Codosiga pulcherrima). The 
Youngs of this is free at first, but finally attaches itself, and 
nes elevated on a pedicle. Then the vase grows _— 
AMER. NATURALIST, VOL. IL 39 
