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31 



Porifera as it is familiar to all, being an article brought into 

 almost daily use for one purpose or another in our domestic 

 economy. By so doing I hope to render the observations on 

 some of the siliceous spongidae clear and more intelligible 

 — but first I must call your attention to a diagram which shows 

 the great difference that exists between the state of the living 

 sponge and that which we are accustomed to see when it has 

 been prepared, bleached and purified and then imported as an 

 article of commerce. 



In its growing state it has a fleshy (or gelatinous) appear- 

 ance and when cut into has some resemblance to a piece of liver 

 or lung. Its surface is studded with innumerable small openings 

 or pores through which a current of water is continually flowing 

 along tubes and canals which intersect and honycomb the body 

 or the sponge in all directions. These lead diiect to the oscula 

 or larger orifices seen on the outer surface ; the first are called 

 the inhalent pores, the latter, the exhalent mouths. As the 

 water flows along the tubes it affords nourishment to the 

 zoophytes — for this sarcode or fleshlike substance is composed of 

 myriads of minute organic cells supported on a fibrous 

 skeleton, each one of which is a perfect and independent 

 organism. After this it bears all effete matter along with its 

 current, to be finally expelled through the oscula. 



How or by what means this flow of water is produced, sus- 

 tained and expelled is not clearly ascertained. Some pysiologists 

 as Dr. Bowerbank, assert that it is by means of minute cilioe lining 

 the canals. The pores of stomata, as they are sometimes called 

 are more or less fringed with spicules; these are so arranged, 

 that, whilst admitting water they prevent obnoxious matter from 

 entering with it to the injury of the animalcules. They have the 

 power of opening and closing their valvular mouths. Many 

 sponges live between high and low water mark, so that when the 

 tide is out the animals by closing their apertures, retain sufficient 

 fluid in iheir tubes to sustain life until the flood returns, to again 

 submerge them. 



There is also another singular property connected with these 

 pores. Whilst examining the amoeba in its young state by the 

 aid of a microscope they are sometimes found to entirely dis- 

 appear from the field of view and fresh ones open in a different 

 place. I have mentioned the word "amceba" and as it forms 

 the sarcode or gelatinous part of the sponge, I will now endeavour 

 to explain its nature and use. 



The sponge animalcule is simply a living cell or cyst pos- 

 sessing the power of secreting a gelatinous substance in which it 

 resides. The young zoophytes expelled from the spongy mass 

 as spores through the oscula are furnished with cilia; or minute 

 vibrating hairs, by means of which they swim freely aboul, until 

 they finally settle upon a spot to grow and fructify. Their ciliae 

 are now lost to sight, they throw out their secretions and as the 

 cells rapidly divide by gemmules, and these gemmules again go 



