ivith some Remarks on the Nature of the Spongiœ Marinee. 379 



moving sporules of the River Sponge cannot be considered as affording any 

 test decisive of their animal natnre ; but, on the contrary, ffom 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 Algœ 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-shajied, 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 theinf. When viewed through a microscope, it is seen that the 

 rapid vibration of the cilia produces a distinct 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. 



X 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 which takes place with the 

 seeds or sporules of the Fuel. Stackhouse in his Nereis Britannica (fasciculus ii.) relates a curious 

 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 papillae or buds coming up from the mem- 



