58 THE EARTHWORM 



in front of the outer seta of the inner double 



row. 



To see these apertures, strip off the cuticle from the 

 anterior part of the worm, and examine the worm with a 

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

 fluid to exude from the apertures. 



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

 the naked eye. They open mid-dorsally in the 

 grooves between the segments, and place the 

 ccelom 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 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 tivo 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 

 cut through these septa close to the body-wall ivith a sharp 

 knife, and pin out the flaps right and left with fine pins. If 

 the worm has been freshly killed, 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, while 

 immediately behind it they are more numerous (fig. 16). 



