176 



ANARTHROPODA 



of three layers are perforated by numerous minute pores 

 for the passage of water and food. The larger sponges are 

 of a more complex nature. 



The body of a sponge in addition to the fleshy material 

 consists in some species of flexible fibers of spongin, such as 

 make up entirely the commercial sponge when purchased. 



In other species 

 like Grantia, 

 lime spicules are 

 present, and in a 

 few kinds, in- 

 cluding the fresh 

 water forms, sil- 

 icious spicules 

 occur. 



The fresh 

 water sponges 

 have a wide dis- 

 tribution, and 

 may be found 

 by looking for irregular more or less lobed cushionlike 

 masses from one to four inches in diamster attached to 

 weeds, logs, and stones in clear springs and ponds. 



Sponges reproduce by eggs and also by internal buds 

 called gemmules. 



In the ocean, sponges are found at depths of from one 

 to six hundred feet. The most famous sponge fisheries 

 are those of the Great Bahama Bank in the West India 

 region, and those of the Mediterranean and Red Seas. 

 All sponges came from the Mediterranean Sea prior to the 

 year 1840, when the famous fisheries were discovered along 



- A fresh water sponge. Photograph natural 

 size. 



