254 ANN U LATA 



B. Internal Morphology 



1. Pin a dead worm on a wax-bottomed pan or on a sheet of 

 cork, or on a soft pine board, and sink it in the water. With 

 sharp scissors cut through the body wall along the median dorsal 

 line. Spread out and pin down the body wall, exposing the 

 internal organs. 



2. Body Wall. 



(1) Thickness? 



(2) Of how many layers does it consist? 



(3) Use of each layer? 



3. Body Cavity or Coelom. Between the body wall and the 

 alimentary canal is a great cavity divided into compartments 

 by the muscular partitions. 



4. Circulatory Organs. 



(1) In a live specimen, find (with the hand lens) the dorsal 



blood-vessel along the dorsal side. 



(a) In what direction does the blood flow? 



(b) Extent of this tube? 



(c) Its branches— how many? These are called ''hearts'* 



or aortic arches. (Segments 6-10.) 



(2) Ventral blood-vessel. Below the alimentary canal, 



find another vessel. How does the blood flow in this 

 blood-vessel — forward or backward? 



(3) Sketch the internal organs, using red for blood-vessels, 



yellow for alimentary canal, and blue for nerves. 

 Make a sketch one inch in diameter, or draw it on 

 the board. 



5. Alimentary Canal, or Digestive Organs. Parts in order: 

 Mouth, pharynx, esophagus, crop, gizzard, stomach-intes- 

 tine. 



(1) The mouth — in somites one and two. 



(a) Shape? 



(b) Size? 



(c) Use? 



(d) Any teeth? 



(2) The pharynx — in somites 2-7. (a), (b), (c) as for 



mouth. 



(3) The esophagus — about somites 6-15. (a), (b), (c). 



