70 PHYLUM VERMES 



The Polypide. Study a number of polypides, both retracted 

 and extended. The forward end of the polypide consists of a cir- 

 cular ridge, called the lophophore, which bears a row of long cili- 

 ated tentacles. In the midst of the circle is the mouth. The 

 tentacles are vibratile and serve as respiratory as well as prehen- 

 sile organs. It will be seen that the lophophore can be entirely 

 withdrawn within the zocecium. 



The Digestive System. The mouth opens into the pharynx, 

 which leads into the oesophagus. This opens into a large saclike 

 stomach, the lower portion of which is lengthened into a long 

 pouch. From the upper end of the stomach, near the base of the 

 oesophagus, the short intestine leaves it and passes to the thick- 

 walled rectum. This leads to the anus, which is situated just out- 

 side the lophophore near the mouth. The digestive tract has thus 

 the shape of the letter V, the point of which is formed by the 

 stomach pouch. Passing from the stomach pouch to the lower end 

 of the body is a broad mesenteric strand called the funiculus. In 

 order to study the digestive tract satisfactorily, a polypide should 

 be found in which both arms of the V come into view. 



The Muscular System. The retractor muscle, whose function 

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

 seen as a delicate strand which passes from the wall of the 

 zocecium 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 tentacles 

 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 cav- 

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

 Spermatozoa develop from the funiculus and, when present, form 

 a mass around it ; they fertilize the ova in the body cavity. 



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 al- 

 ready stated, the entire colony, with the exception of its oldest 

 member, has developed in the latter way. 



