DISSECTION 5& 



pocket lens, squeezing it slightly so as to cause the ccelomic 

 fluid to exude from the apertures. 



e. The dorsal pores, thougli small, are often visible to 

 the naked eye. They open mid-dorsally in the 

 grooves between the segments, and place the 

 eoelom in communication with the exterior. 



The first one is between segments x. and xi. 

 and opens into segment xi. Behind this point they 

 occur regularly in every intersegmental groove. 



II. DISSECTION OF THE EARTHWOEM. 



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. Gut 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 

 cut through these septa close to the body-wall, and pin out the 

 flaps right and left with flue pins. If the worm has been 

 freshly hilled, immerse it for a few minutes in spirit. 



A. The Septa. 



These are incomplete transverse membranous partitions, 

 connecting the alimentary canal with the body-wall and 

 dividing the body-cavity into segments. They are placed 

 opposite the grooves on the external surface 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 shifted backwards so 

 that they are less numerous than the external rings, whilff 

 immediately behind it they are more numerous (fig. 23). 



B. The Digestive System. 



The aUmentary 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 hps and no 



teeth. 



