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 zow- 
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 owecia. These are peculiar structures, found in 
connection with the zocecia, 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 zocecia 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 
