LUMBRICUS TERRESTRIS L. MULLER 91 



dinal muscles is to shorten the body when all bands contract 

 simultaneously or to curve it in the direction of that band which 

 contracts singly. In this case the opposite bands act as antag- 

 onists. 



The chetas or bristles sit in special sacks formed by a depres- 

 sion of the hypodermis. The base of the sack is connected with 

 special muscle fibres. These fibres serve to move the chetae thus 

 helping in locomotion. 



Coelome or body cavity. The body cavity of Lumbricus, 

 inclosing all organs, is divided into chambers by transverse 

 intersegmental septa. The septa are lacking only in the anterior 

 six segments and the last posterior one where they are replaced 

 by a loose network of muscular and connective fibres. The septa 

 have a muscular structure and the peritoneum which lines the 

 body wall extends over all septa. The body cavity is filled with a 

 liquid containing amcebocytes and chloragogue cells which will be 

 mentioned in connection with the digestive system. Each 

 ccelomic chamber communicates with the outside through a pair 

 of nephridia and a dorsal pore. The dorsal pores have been 

 already mentioned. If a worm is subjected to a strong stimulus 

 or irritation a drop of ccelomic fluid appears from every dorsal 

 pore. It is probable that we have herein an arrangement to keep 

 the surface of the worm moist in case of excessive dryness or 

 heat. 



Digestive organs. The alimentary canal runs in a straight 

 line from the mouth to the anus. It begins with the mouth 

 cavity. This is followed by a muscular, ovoid pharynx which 

 extends to the end of the sixth segment. The pharynx is pro- 

 vided with numerous muscles attached to the body wall and 

 acting as dilators. The oesophagus is a laterally compressed tube 

 extending as far back as the thirteenth segment. In the eleventh 

 and twelfth segments it receives three pairs of small calciferous 

 glands. These glands secrete calcium carbonate. The oesopha- 

 gus is surrounded by five pairs of "hearts." The crop has the 

 shape of an ovoid with a diameter several times that of the 



