XIV. SPONGES 



Limy Sponge (Grantia). 



The sponge is the simplest 

 of all Metazoa. One of 

 the commonest forms is 

 Grantia, a tiny urn-shaped 

 object found in salt water 

 attached to piles or stones. 

 It is abundant in 

 Island Sound. 



Long 



For this exercise have small 

 vials containing specimens of 

 Grantia preserved in formol 

 or alcohol. The body is at- 

 tached at one end. What do 

 you find at the opposite end ? 

 Label the hole the osculum. 

 This leads into a cavity called 

 the cloaca. The wall of the 



Grantia, a limy sponge, on the shell of a mussel. 

 From photograph loaned by American Museum of 

 Natural History. 



body is pierced by a number of tiny holes or pores 

 which communicate with the cloaca. The shape of 

 the sponge is maintained by a skeleton composed 

 of many tiny pieces or spicules of carbonate of lime. 

 Notice the edge of the osculum. Make a drawing 

 of the Grantia twice natural size, showing all the 

 above structures.' 



An examination with the microscope 

 shows the pores of the sponge to be lined 

 with ciliated cells. These, by means of move- 

 ments of the cilia, set up a current of water 

 toward the cloaca. This current bears food 

 particles, tiny plants and animals, which are 

 seized and digested by the ciliated cells. 

 T^. r . . These cells seemingly pass on the food to the 



Diagram of a simple sponge; <=> ^ i 



t.inhaiant opening; o, ex- Other cells of the body. The middle layer 



halant opening or osciu- 



lum. 1 See Hunter and Valentine, Manual, page 159. 



191 



