CLASS ANNELIDA. 



38 



FIG. 44. 



walls of which the products of digestion reach the body 



cavity, without the intervention of 



a circulatory system. A series of 



muscles enables the animal, on be- 

 ing irritated, to retract itself into 



its supporting cup, where, by draw- 

 ing a lid over the top, it may seal 



itself in.* 



Polyzoa deposit large numbers 



of eggs, each of which is capable 



of producing a new colony. The 



hard, limy shells have been found 



in the oldest fossiliferous rocks. 

 The Brachiopods are also found, 



both fossiled, and still living in the 



ocean. They were long supposed 

 allied to the oysters and 

 Recent investigation has 



shown their unique struct- 

 ure. What were the long 

 tentacles surrounding the 

 mouth of the Polyzoa, 

 have in the Brachiopods 

 united into two groups 

 which are supported by 



" arms " ; these in some 

 forms are coiled in a 

 spiral. These arms, giv- 

 ing the name to the group, 



to be 

 clams. 



Pa lu di eel' la eh ren her' gl I. 

 Polyzoon, with its tentacles ex- 

 panded. 0, (Esophagus. S, 

 Stomach. 



FIG. 45. 







Section through Brachiopod, showing anatomical 

 peculiarities. U, The upper shell separated from 

 the lower at the opening. O. J/, Muscles which 

 close the valves P, Peduncle, by means of 

 which the animal attaches itself. A, The so- 

 called spiral "arm." 



* Some genera have attached to the exterior of the capsules long whip.*, 

 which keep up a continuous lashing, while others have organs resembling the 

 head and beak of a bird. These open and close until they finally grasp some 

 small object, when for a time they seem satisfied. The real use of these organs 

 is not known. 



