X. 



NOTES ON SPONGES, RECENT AND FOSSIL. 



By Henry Gilbertsox. 



Jiead at Hertford, 2ith February, 1880. 



It may not have occurred to many of my hearers that we at 

 Hertford shonld have any local interest in sponges. Nevertheless 

 such is the case. All our roads and paths are made of flints, and 

 many of our churches and walls are built of the same kind of stone. 

 All Saints' Church and St. Andrew's Church, at Hertford, and 

 St. Mary's, at Ware, are examples. Now, it will be my endeavour 

 this evening to prove to your satisfaction that most of these flints 

 are fossil sponges or enclose allied forms of animal life. Beyond 

 our local interest in sponges in their fossil state, we have also an 

 interest in them in their recent state. We will, therefore, first 

 glance at them in their recent forms. 



There are several species of sponge in use for economical pur- 

 poses, chiefly obtained from the Mediterranean, and known as 

 Turkey sponge ; a common variety is also used which comes from 

 the West India Islands, and is known as Bahama sponge. The 

 trade in sponges is very considerable, and is carried on chiefly by 

 Turks, Greeks, and the inhabitants of the Bahama Islands. The 

 sponges are found at a distance of 1,000 to 2,000 yards out at sea, 

 on banks of rocks formed by molluscous debris. The finest 

 specimens lie at a depth of from twelve to twenty fathoms, those 

 collected in shallower waters being of inferior quality. 



Sponges are not fit for economical purposes in the state in which 

 they are taken from the sea, inasmuch as the animal matter which 

 secretes them must be got rid of, and to effect this they are buried 

 for some days in the sand, and are then soaked in water, and washed 

 in some instances by stamping with the feet until all the animal 

 matter is thoroughly got rid of. Thus far we have only spoken of 

 the sponge of commerce. There are, however, many other varieties, 

 and the sponge family has been grouped by naturalists into three 

 orders — namely, the Calcareous or Chalky Sponges, the Siliceous 

 or Flinty Sponges, and the Kei-atose or Horny Sponges. 



These terms bear reference to the skeleton of the sponge ; for 

 instance, the keratose or horny sponge is the sponge of commerce of 

 which we have been speaking. 



Let us now consider what secretes or builds up the skeletons. 

 When any variety of sponge is brought alive from sea- or fresh- 

 water it is found to have a large amount of jelly-like substance, 

 called sarcode, surrounding and enveloping the skeleton. Upon 

 examining a small portion of this substance with the microscope, it 

 is found to resemble in many respects that low type of animal life 

 known by the name of Amoeba, the typical genus of the Amoebina, 

 found both in salt- and fresh-water, frequently among decaying 

 vegetable matter. 



VOL. I. — PAKT 1X1. 7 



