THE ANIMAL LIFE OP THE GROUP. 499 



some forming- tubes for their habitations, while still others are noted for mak- 

 ing paper-like tubes. Some species burrow beneath the sand and mud; others 

 fasten their tubes to stones or coral and cover them with sand or bits of shell. 

 Another group of worm-like animals ^^ may easily be found by breaking 

 up old coral rocks in which they are able to drill round holes. In the common 

 forms ^* the anterior part of the body can be drawn into the posterior part. 

 They are tough and leathery, lilunt at the tail, and taper gradually to the end 

 of the proboscis. 



Sponges. 



It is a matter of regret that the many species of sponges ^^ that occur on 

 oiir reefs and to moderate depth in the water about them have never been 

 systematically collected and studied. This need not prevent one from ad- 

 miring and examining them, however, not only on their own account, but on 

 account of the large number of worms, crustaeea, starfish and other animals 

 that enter them for protection. 



There is scarcely a stone of any size on the reef that is without one or 

 more of these curious creatures attached to it. Red, black, white, yellow and 

 purple sponges are common, but almost every color one can suggest is repre- 

 sented. Many of them are shapeless encrusting masses; still others have a 

 definite form, so familiar as to render their identification complete at a glance. 

 Still others look more like weird plants than animals, and it is not strange 

 they are often mistaken for such, when we consider their irregular plant-like 

 growth. Although they were once claimed by botanists as part of the plant 

 kingdom, they are now generally regarded as representatives of the simplest 

 form of the many types of many-celled animals ^^ as distinguished from the 

 single-celled animals,-''''' which are nearly all microscopic. 



Sponges are free swimming animals for only a very short time, at an early 

 stage of their development. They soon become attached to some object, and 

 not infrequently modify their form so as to conform with the shape of the 

 object to which they adhere. For this reason they seem to have no fixed shape 

 of bod.v, as individuals of the same species vary greatly. 



The sponge is a very simply-organized animal and lives a very simple life 

 indeed. Their food is the mim;te organisms in the water. Currents are 

 created in the animal by means of minute flagella which wave to and fro in the 

 tiny tubes that lead into the animal through small pores scattered over its 

 body surface. The food is digested out of the water before it is allowed to 

 pass out again throxigh the large holes ^'- distributed over the animal at irregular 

 intervals. Sponges arc of considerable interest to zoologists, as they are the 

 lowest types in which cells are found differentiated for certain i)uri)oses, as 

 skeleton cells, reproductive cells, and so on. 



Sponge culture has never been attempted in Hawaii, though the subject 

 has been occasionally discussed. While none of the species now growing on 



83 Gephyreo. "** Sipunculojdea. ^^ Porifera. ^e Metazoa. ^^ Protozoa. 38 Qscelum. 



