A SPONGE 147 



Specialized reproductive organs are not present in Grantia. 

 The sexual elements will be found in the form of large, spherical 

 bodies buried in the wall of the sponge. Fertilization takes place 

 here, and when development begins the young embryos escape 

 into the sea water through the canals. For a while the embryo is 

 a free-swimming animal, but it finally fastens itself to a rock and 

 develops into the adult sponge. Besides this sexual reproduction, 

 the sponge also reproduces asexually by budding. Each distinct 

 cluster of individuals probably represents the gemmated progeny 

 of a single individual. 



Special respiratory, excretory, digestive, circulatory, nervous, 

 and locomotory organs are wanting in Grantia. Respiration and 

 excretion are carried on through the entire surface of the body. 

 The animal feeds on minute organisms and particles of organic 

 matter suspended in the water which streams into the canal sys- 

 tem through the incurrent pores. The radial canals are lined with 

 peculiar entoderm cells called collar cells, each one of which 

 possesses a flagellum. The action of the flagella produces the 

 current of water through the canals, from which the collar cells 

 obtain and ingest food particles. Circulation is from cell to cell. 



