skeleton of an animal, but his research was again ignored by later 

 generations. Between the fourth century b.c. and the eighteenth 

 century a.d. sponges were variously held to be plants, the homes 

 of marine worms, the work of "some kind of sea insect," or soli- 

 dified sea foam. Not until 1786 was their animal nature again stated, 

 this time by an Englishman, John Ellis, after he had noticed jets 

 of water coming out of the round holes of a living sponge that he 

 had placed in a bowl of sea water. As late as 1841 at least one 

 well-known naturalist was still arguing that they were plants. 



It is easy to understand why there was so much disagreement 

 about the nature of sponges. Apart from the unicellular animals, 

 they are the lowest on the animal scale. A typically marine inverte- 

 brate, the like of which is not found on land, the sponge is also 

 one of the most peculiar animals in that it remains fixed throughout 

 life, except in its larval stage. Here we have another marked differ- 

 ence between Ufe on land and life in the sea. The bottom of the sea 

 is populated not only by animals that crawl or burrow but by many 

 that are fixed, plantlike, on the sea bed. Some zoologists now agree 

 that we should regard sponges not as animals but as animal-like, 

 that we should think of them as belonging to a separate subkingdom 

 of the animal kingdom (the Parazoa). 



The reasons why sponges should probably be set aside from the 

 main stream of animal life make a fascinating study for the specialist. 

 The body of a sponge is not made up of tissues composed of layers 

 of cells in the usual way, but of a network in which individual cells 

 have special functions. This network is crisscrossed by a labyrinth 

 of fine tubes marked at intervals by pumping chambers. The 

 economy of a sponge is very simple. The pumping chambers draw 

 streams of water in through fine pores in the skin, pores that are 

 invisible to the naked eye. This stream brings in food and oxygen, 

 and after flowing through the body it is pumped out through 

 larger openings on the surface, carrying waste products along with 

 it. Because the incurrent pores are so tiny, the sponge can draw 

 only fine particles inside itself. Thus, since the food of at least 

 some sponges consists of bacteria and very small specks of dead 

 animals and vegetable remains, they play a scavenger role in the 

 economy of the sea. 



Although some sponges are annuals, others seem to qualify for 

 a place among the immortals. Few animals feed on this group of 

 sponges, and the wounds caused by those that do are readily 

 repaired. If a crab pulls a sponge to pieces, each fragment can 

 grow into a new sponge. A piece of sponge pressed through fine 

 silk can be separated so that all its cells lie individually at the 

 bottom of a glass dish. But within two to three days the individual 

 cells will have joined to form small masses of cells, each able to 

 grow into a new sponge. In addition, two nearby sponges may 

 grow toward each other and, when they touch, join to form one 

 huge sponge. 



The stories of the eel and the sponge are very much the same in 

 that they show that our understanding of living creatures in the 

 sea does not come about spontaneously and suddenly. Our learning 

 process is a painfully slow one, and the efforts of dozens or, more 

 often, hundreds of researchers ranging over an equal number of 

 years are usually required before we come to an understanding of 

 how even the simplest organism lives. And the search is endless. 



In 1765 the biologist Jotin Ellis proved that 

 sponges were not dead structures by ob- 

 serving their inhalent and exhalent currents. 

 This one, which he found off the coast of 

 southern England, he called Spongea palmafa. 

 Apart from the single cell animals, sponges 

 are the lowest on the animal scale. 



81 



