with some Remarks on the Nature of the Spongiæ Marine. 379 
moving sporules of the River Sponge cannot be considered as affording any 
test decisive of their animal nature; but, on the contrary, from the manner in 
which they began to vegetate, I am most fully authorized in holding them to 
possess far greater affinity with certain seeds, which are well known to belong 
to several Ælgæ or Cryptogamous plants. 
I will now offer to you a few remarks on the locomotive germlike bodies 
of the Sea Sponges, as observed by Dr. Grant, because they bear so consider- 
able an analogy with those similar bodies, of which I have before given a 
separate detail. 
That acute naturalist has called them the ova of the Sponges, and has de- 
scribed them* as being quite visible to the naked eye, of a yellow or amber 
colour, somewhat translucent, egg-shaped, and tapering more or less at their 
narrow end. "Their whole outer surface is covered with delicate projecting 
cilia, except their smaller extremity or base, which is supposed to be entirely 
destitute of themt. When viewed through a microscope, it is seen that the 
rapid vibration of the cilia produces a distinet current in the water, which 
always flows from their rounded towards their tapering end. They swim 
about by means of these cilia, always carrying their broadest extremity or 
top forwards: they glide along with a regular and smooth motion; sometimes 
they come to the surface, and sometimes revolve round their axis. At length 
they fix themselves to a favourable spot, and, losing entirely their original 
form, become a flat transparent film, through which the fibres shoot. 
* The above description is abstracted from Dr. Grant's accounts published in vol. xiii. p. 382 of the 
Edinb. Phil. Journ. for 1825; p. 154 of the Edinb. New Phil. Journ. for 1826; and p. 129 of the 
same Journal for 1827. 
t See figs. 26—29 of plate 2. in the Edinb. New Phil. Journ. for 1827. 
t All the germlike bodies of the Sponges and the gemmules of the Zoophytes swim with their 
rounder ends or tops precedent. The reason of this I believe is, that those ends are the lightest; and 
their lower or tapering extremities, being filled with the opake and vital substance, are consequently 
the heaviest. 
$ This mode of growth and development very greatly resembles that whieh 2 place with ithe 
seeds or sporules of the Fuci. Stackhouse in his Nereis Britannica (fasciculus ii.) relates a . 
experiment on the germination of the sporules of some species of Fucus, and adds, In less than a 
week a thin membrane was discoverable on the surface of the pebble, where the seeds had lodged, 
with the naked eye; this gradually extended itself, and turned to a darkish olive colour. It con- 
tinued increasing in size, till at last there appeared mucous papille or buds coming up from the mem- 
