110 



THE EARTHWORM 



divide the coelom into chambers one behind the other. What is the 

 relative position of the septa and the external constrictions between 

 the somites? 



(c) Continue the cut forward as far as the second somite; carefully 

 separate the edges of the body wall and pin the edges as before. How 

 do the anterior septa differ from the others? Have they any different 

 use? With the aid of Fig. 53 identify the following regions of the 

 digestive tract, beginning anteriorly: pharynx, esophagus, crop, giz- 



Cforso-intestina/ 



par/eta/- 



nephridium 



in tee tine - 



ventro- 

 inteatinal i/ee^t 



ventro-tegumentai^y 

 ves^ei 



,.-c6e/om 



seminal vetic/e 

 dorsa/ \/e5s,e/ 



fyeort- 



esophagus' 

 fatcra/v'essd- 



ventral Kesse/ 

 /aterai- neural ves&el- 

 ^■xsubneurai vessel 



ybody wall 



dorsal vesee/ 



XIV '• XIII 



par/eta/ veeee/ 



heart 



Anterior 

 end 



3ubneura/ ves£>G/ vent'ra/ ve^se/ /otera/ i^eeeeJ 



Fig. 54. — Circulatory system of Lumbricus terrestris] diagrams to illustrate 

 the relations of the vessels and the course of the blood, as shown by arrows. 

 A, cross section in the region of the stomach-intestine. B, cross section in 

 the region of the hearts. C, lateral view of vessels in somites VII to XIV. 



(Redrawn from J. B. Johnston and S. W. Johnson, 1902, American Naturalist, vol. 36) 



zard, and stomach-intestine. Check with instructor if you do not see 

 each of these regions clearly. Other structures present in this region 

 are parts of the reproductive system. The so-called hearts, or pairs 

 of blood vessels which connect the dorsal vessel to the ventral blood 

 vessel which lies beneath the digestive tract, are located in somites 7 to 

 11. Dorsal to the pharynx in somite 3 are two small white bodies, 

 the dorsal ganglia. In all but a few of the anterior chambers of the 

 body cavity, there are paired fluffy masses on each side. These are the 



