A BRYOZOAN 87 



The muscular system. The retractor muscles, whose function 

 it is to draw in the lophophore, may, in favorable specimens, be 

 seen as delicate strands which pass from the wall of the zoce- 

 cium to the pharynx. 



The nervous system has not yet been observed in Bugula, but 

 in nearly allied Bryozoa it consists of a single ganglion between 

 the mouth and the anus. From it nerves radiate to the ten- 

 tacles and other organs. There are no organs of special 

 sense. 



The reproductive organs. The animals are hermaphroditic. Ova 

 develop from the peritoneal lining of the spacious body-cavity 

 and will be seen, when present, lying near the stomach pouch. 

 Spermatozoa develop from the funiculus and, when present, 

 form a mass about that organ. 



There are two methods of reproduction, the sexual, in which 

 the new individual develops from the fertilized egg^ and the 

 asexual, in which the new individual arises by budding. As 

 already stated, the entire colony, with the exception of its 

 oldest member, has developed in the latter way. 



Exercise 2. Draw an extended individual in which the entire 

 digestive tract can be seen and label all the organs observed. 



There are no special respiratory or excretory organs; the 

 entire outer surface of the body performs these functions. The 

 circulatory system is represented by the colorless blood fluid 

 alone. There are no circulatory vessels, the blood being 

 contained in the body-cavity. 



Avicularia and ocecia. These are peculiar structures, found in 

 connection with the zooecia, which are morphologically equiva- 

 lent to distinct individuals. An avicularium is a small structure, 

 like a bird's head in shape (hence the name), which may be 

 found attached to the wall of some of the zooecia near the open- 

 ing. It has a movable lower jaw which can be opened and shut 

 by two sets of muscles. Its function is to seize and hold small 



