124 Invertebrate Zoology. 



Make drawings of the head as seen from the side and from 

 below. 



The segments immediately following the head, the pro-, 

 meso-, and meta-thoracic, are each provided with a pair of 

 jointed appendages, the thoracic legs. 



Behind the thoracic region, the abdomen extends as a 

 series of ten segments. Do the first two abdominal seg- 

 ments bear appendages? The fleshy appendages of the 

 third, fourth, fifth, and sixth abdominal segments are called 

 i\\t pro legs. Note that each is terminated at its free end by 

 a series of hooks. The seventh and eighth segments are 

 not provided with appendages, though the eighth frequently 

 bears a median dorsal spine. The ninth segment is short 

 and somewhat suppressed, while the tenth is pierced by the 

 anus and bears a pair of anal prolegs. In the embryo all 

 the abdominal segments are provided with rudimentary 

 appendages. 



Extending along each side of the animal are a series of spir- 

 acles, openings which lead within the animal into an elabo- 

 rate system of branched respiratory tubes or tracheae. The 

 spiracles do not occur on every segment, but are present 

 upon the first thoracic and upon all the abdominal segments 

 except the ninth and tenth. 



Make a drawing of the animal as it appears when viewed 

 from the side. 



Internal Anatomy. With a fine pair of scissors cut 

 through the integument, along each side of the animal a little 

 above the line of spiracles, from the side of the head to the 

 ninth abdominal segment. Remove the dorsal piece without 

 disturbing the underlying viscera. 



