70 THE EARTHWORM. 



lines to represent the septa ; and draw the anterior part of the 

 worm from below about one line, leaving the sketch of the dissection 

 to be drawn about the other. 



II. DISSECTION OF THE EARTHWORM. 



Extend the animal under water with the dorsal surface 

 upwards, fixing it down by two pins through the sides of the 

 fourth segment and two near the hinder end. Cut through 

 the body-wall from end to end, close to the mid-dorsal line. 

 Gently raise the flaps with the forceps, and note the trans- 

 verse septa dividing the body-cavity into segments. Carefully 

 pin out the flaps right and left with fine pins, stretching them 

 well as you do so. 



It will save much time in determining the positions of 

 some of the important organs if the pins are placed in definite 

 segments say the tenth, fifteenth, and twentieth. 



A. The Ccelom. 



The ccelom, or body-cavity, is a large space, within which 

 the alimentary canal and other viscera He. It is divided into 

 segments by transverse septa, which connect the alimentary 

 canal with the body- wall. The septa correspond to the ex- 

 ternal annuli throughout the whole length of the body, except 

 in two regions : (1) in front of the fourth segment, where they 

 are absent ; (2) in the region of the gizzard, where they are 

 slightly irregular in arrangement. The ccelom contains a 

 fluid with numerous amoeboid corpuscles. 



B. The Digestive System. 



The alimentary canal is a straight tube running from the 

 mouth to the anus, and is divisible into the following regions : 



1. The buccal cavity is small, and is situated in the first 

 three segments. The opening of the mouth in the 

 ventral part of the first segment has soft lips and 

 no teeth. 



