128 THE BIOLOGY OF THE ASTIMAL 



the septa divide the body-cavity into smaller cavities. It 

 is well to have also a second, vsrell-hardened specimen, 

 whose body has been divided accurately along the 

 middle line, thus making a longitudinal section through 

 the entire alimentary canal to show the internal ar- 

 rangement of its parts. 



a. The body-wall. — Of what is it composed ? How 

 many layers are distinguishable? What is its 

 color ? Are all of the layers of the same color ? 

 What relation has the color of the body-wall to 

 that of the surface of the body ? What varia- 

 tions in the thickness of the wall ? Does it con- 

 tain any bony or shell-like bodies % 



With a sharp knife cut a well-hardened speci- 

 men in two at the most muscular portion of 

 the body. Then cut a thin transverse section 

 and lay it on a slide in a drop of fifty per cent, 

 alcohol or glycerine, and examine with a low 

 power. Note the layers of the body-wall, es- 

 pecially the circular and longitudinal muscles, 

 the latter projecting like a fringe into the body- 

 cavity. 



h. The body-cavity. — How is it formed? What 

 organs does it contain ? Is it a continuous 

 cavity? Has it any communication with the 

 exterior ? Kill a worm by drowning or by ex- 

 posure to chloroform vapor under a tumbler, 

 cut through the body-wall of some of the poste- 

 rior segments, and with a pipette or a glass rod 

 collect some of the fluid (peri -visceral fluid) 

 found in the body-cavity. What is the color 

 of the fluid ? Is it very abundant ? Put a drop 



